Bad karma going for revenge. Will leave you feeling bitter regardless and that means he continues to have a hold on you. That being said catholics, devout ones at that, are the dumbest of all people on earth. Subscribe him to protestant weekly or something that should get his goat in a non bad karma war. Ive loads more ideas but sounds like you should be putting your energies into your girl with this evil cancer!!!! Peace bro and I hope she recovers.
So you want to fuck with him because your ex girlfriend was irresponsible and didn't handle her business? It wasn't his responsibility to deliver her mail. Had she had her addresses changed correctly then she wouldn't be in the situation. Some people refuse to take responsibility when it is easier to blame it on "the bad guy". If it was me anything addressed to my ex would go in the garbage without being read at all. A divorce means I don't have to take care of you or your bs any more.
He must feel really bad about what's happening, especially if done out of spite. He fucked up, no need for you to do the same. Stage Three can be beaten.
I know how mad you must be OP, despite everybody in here acting like they've never been so upset at being helpless before. But indeed you are helpless because getting revenge isn't going to bring that money back. So now you have to be willing to work twice as hard for her behalf and her son. Just stay calm, cool and collected. She can't see you freaking out, it'll only make matters worse. But dont forget to take a breather and get your frustrations outs privately, safely and productively. And legally of course. Trust me I know it's a hard pill to swallow when you have to accept shitty situations like these. Good luck to you and your family.
if what you say is true, file a lawsuit. that will make anyone miserable. don't be an idiot for asking this kinda stuff online and call a lawyer.