scammed? how to handle this situation?

OK so I have been smoking weed about a year now, and I have become known amongst my friends for being one of the best at eyeballing weights pretty well. So today I went to pick up a Q off my dealer. When I asked if he had any he said yes, but when I met him he was with his friend and said that it was his friends weed (not my dealers). So I ask to see the weed and so Im there holding the bag out in public checking out my purchase.. And it didnt look too amazing as the dank im usually getting but it was pretty standard weed. I didnt care cos weed is weed and fair enough he didnt have any and got his friend to hook me up for the occasion. Upon seeing the bag I realised it was very fucking different to the Qs I normally get, it looked like alot less.. So I told both of them there and then,, "This looks pretty light for a Q" and hes like dude put the bag away its looking suspicious. So I put the baggie in my jacket and asked "are u sure this is a Q?" and his friend answers" yeah man its 7 grams i scaled it" I told him it doesnt look like it and he answers with the usual BS "nah dude the buds are heavy.." I just wanted to get out of there so I paid him and bounced. Probably a mistake but this dealer is more of a friend than a guy who sells weed to me so I just put a little faith in him paid and left.. Now when i get home. I just slammed the bag on my scales and it said 4.4Grams (with the plastic baggie!) so without any time waste - less then 30 mins after i paid for the stuff I messaged him asking what the fk is going on and sent him a pic of the weight.. 
 
Anyways he apologised and told me "its good stuff though" I told him Im not interested in the quality at this point "I asked and paid for 7 grams so I should get 7 Grams" he said he will see if he can get me another Q tomorrow. So I rang him after a while since Im wondering how this is gonna work.. If I am gonna  swap the old Q for the new Q or if he gonna hook me up with extra 3 grams or what?? so I ring him and he says hes busy but he will ring me back.. its been a good 20 minutes and he still hasnt rang me back? Should I be worrying?
 
Also I have alot of info on both of these guys and could potentially track both of them to their house / fuck them up, however I do not want to resort to this since I believe we can solve this problem.. this kids shit pisses me off tho, I am gonna only deal with adults from now on, shame this herb is illegal and we have to go through this kind of shit
 
 
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Update:
 
Alright guys. Some progress has been made with this situation. This is a good story so listen up blades.. *inhales*
 
I messaged the guy about once every 2 days reminding him that I needed compensation for the shorted grams. He wouldnt reply at all, at this point i had a complete Dox of him so I knew where he lives, who he lives with, his phone number, education etc. Anyways I used this information to successfully locate his house on google maps and took a picture of it with street view. I then decided it was best to leave this alone and cut my losses and forget about this said person. Then one day I get on my phone and hes online on WhatsApp. 
 
At this point I believe its a lost cause, so for some comedy I said "happy ramadan" and someone replied in arabic, so I knew it wasnt him. It was actually his friend, the one who provided the weed last time which was a whopping 3grams short. Anyways his friend was basically taking the piss in arabic saying stuff like "where are you? your house got destroyed" in arabic which made no sense so I guess he was drunk or very high. These guys know barely anything about me, except my nickname (far from real name) and the town I live in (it's big) and a couple of mutual friends who are very loyal and I can trust. Anyways since we were on the topic of houses I thought it would be funny to drop him a picture of his friend's (the dealers) house (courtesy of google maps street view). This guy, who hadnt replied at all for 2 weeks, and completely ignored me suddenly went nuts. The conversation went a little like this:
 
Me: sends pic of house
dealer: What the fuck are u doing with a picture of my house bro? are you stalking me or something?
Me: No, but I thought that might get your attention
dealer: If you wanna get my attention then fucking come talk to me bro. Why the fuck have you got a picture of my mums fucking house bro??
Me: You said you were gonna give me a call. But that didnt happen
dealer: Is this you trying to threaten me bro. is that why you have gone and stalked where I live? What do u want from me man. DO u wanna come rob my house or something?
Me: I didnt "stalk" you, anyone can find out this information. You're not very careful
dealer: Neither r u? If ur not lucky bro. If u try to put my familys home in jeopardy. Then wallah bro this wont end out too well and I thought we had a friendly relationship?
Me: Look *his name*, Im not a dickhead ok. Our relationship is a business one and a friendly one too. Im not out here to fuck you over. But when u scam me twice I don't appreciate it at all. And when I talk to you about it, you don't reply. And I am not making any threats, I can just give *his mothers name* a call and ask for my money if I want. Or you could start replying and we can figure it out respectfully.
dealer: If you want to be respectful, dont go sending me pics of my house if u want to talk about this and wish to draw a mutually beneficial conclusion then I advise we meet tomorrow or after tomorrow and discuss this face to face.
Me: we can discuss a mutually convenient solution here. There is only one solution to this.. You either pay me back for the missing grams or replace them and we're good. Im not trying to fuck u over, just trying to get what I paid for
dealer: I think it would be a considerably better idea if we can talk about this free from the heroics screen based communications seem to bring about. We'll meet and we'll both leave smiling.
Me: I'll give you a call some time soon, take care
dealer: take care bro
 
OK so #1 rule is never to meet dealer by urself in a situation like this, so I am obviously not going to meet him alone if at all. I am not really afraid of him, he's only 1 year older than me, and not much bigger. But he does know alot of people. This is the UK so there is no guns or anything like that and I doubt he would fight me over £50... But just to be careful Im gonna ask my MMA fighter friend and his bro's to come with me just in case and maybe we can actually sort this out. I need your opinions on best way forward from here GC! Hopefully I can get justice 

 

Also I should add I am good at doxing people/ finding out as much info on them as possible online.. and I have already tracked down the guy who sold me the light bag to one of two addresses and telephone numbers.. If he doesnt sort this out I will be calling his parents anonymously to let them know their little boy sells weed and he likes ripping people off

 

Thanks guys for the replies. I understand that the most mature thing to do is just to stop talking to the said person and no longer trade with them. However if every time they rip somebody off thats the only retribution they get then they are going to rip people off for a long damn time. The thing is I know that in any black market there are no rules and people will rip you off at any given opportunity but the fact this guy look me in the eyes and tell me twice its 7 grams then he shorts it not one, not two but three grams?? I think he is having a laugh at the fact he think he can get away with this..
 
I don't have a steady income at the moment and this kind of behaviour really just pisses me off. I am not a fighter but I am not someone to be fucked about like this. I have many friends who got my back and I know alot of shady people who will do bad things to this guy if I told them about this.. for now I am going to be patient and smoke a bowl right now since I need to chill out a bit.. But if we dont reach a resolution soon things might get ugly.

 

Thanks for the advice guys, I agree actually now that violence doesn't actually solve these problems and if anything I only want to see him suffer because of how angry he made me. Not about the money/weed but based on the principle of scamming a friend. I see now that revenge probably wont work since it will just create a cycle. But look at this: both these guys have very little info on me. I go by a nickname in real life that has no relation to my real name and I have never once brought a dealer remotely close to where I live just in case shit ever happened. I have both these guys full names, addresses and tel nos after doing a bit of research.. I could wait a week, maybe even two.. Ill give the guy a chance to refund me or fix things but if not, what is the harm of just ringing his home number anonymously from skype through a VPN and either:
 
1. have a short word with his parents about their son. (His parents are pretty strict muslims who will most likely punish him)
2. Ring up and scare him, pretend I am from the authorities and scare him off for a bit just as a bit of payback.
 
I do honestly want to let him off the hook and just forget about him but at the same time I dont want to do nothing about this because this chump deserves whats coming to him.

 

yeah bro, people who don't value customers are going nowhere fast. Id rather deal with businessmen and herbalists than thugs who want to make a quick buck.

 

alright so its been 2 days and still no reply from the dealer or his friend so I have decided I am gonna take action pretty soon if he keeps ignoring me. I am gonna call the kid's parents and tell them a little they don't know about their son.. should make his life hell for a good week or two and that's plenty for me.