Not sure what to do anymore!

my ex husband has not stopped with the name calling over the years (over 9 years separated and divorced) and i still get extreme anxiety about it all. My 2 boys are horrible when they have been around him and they come home and the do and say completely inappropriate things usually at school. the school know how hard myself and my (now) husband are trying to do the right thing by the boys. They are both diagnosed ADHD and on medication but the younger one seems to be the most affected with his emotions. We stopped visits around this time last year when things started to get really out of control. he wasnt adhering to the boys medication needs amongst other things so we said no overnight visits. We didnt stop him from seeing them at all but that is pretty much exactly what he did! he went into rehab for 5 weeks and i gave him the benefit of the doubt after an unsuccessful mediation where he claims we are dictating to him when he can and cant see the children. in actual fact, the kids have afterschool sport and sport on weekends that he doesnt bother to help with at all! Mediation suggested that he helps but he hasnt. He goes on holidays and buys expensive toys for his hobbies but wont pay the thousands he owes in child support... mind you we used to only get $30.mth for years as he owns his own business! He has written into the concrete in the past that the youngest child is a wanker and he called his eldest step daughter a slut guts on her facebook page (she is a teenager) I am just so sick of it. Plus I am afraid he wont return them one day (which has happened in the past). Its making me into a horrible mum and taking it out on them and the rest of my family which i know doesnt help anyone. He takes them when he wants them plays with them and sends them home (usually broken). I had to ask my husband to step up and tell him to show me some respect to which my husband was abused with a barrage of text messages. i just wish he was dead!