Divorce Support Forums: verbal abuse and threats from ex over child suppor

Wow. This is a doozy-and my first time posting.
Been divorced for many years. X is on 3rd wife (I'm first, 2nd is in hiding). X is emotionally unstable and becoming verbally aggressive/threatening(extremely). Since I am remarried and financially stable, for years things were tolerable and child support was not made an issue. He never provided proof of income (on which to base CS) and we didn't push so as to avoid the certain verbal assault. (He is basically good to our child, and we have tried to keep the peace so their relationship would stay stable)
He recently remarried, claims disability and he and his new spouse do not work. He had a desk job and has chosen to persue his dream of becoming a rock and roll star. (Not joking) His inability to earn a living is seriously questionable due to the fact that he now travels and performs on stage, rather than his previous desk job. He shows minimal interest in our child (Thank God), and seems to only "claim" his visitation rights when he feels like it.
CS has been sporadic, sometimes checks bounce, and he refuses to reimburse his portion of medical expenses for our disabled child, even though ins. co states that reimbursement was already issued to him. He disputes this fact, and states that I actually owe him thousands in overpayment because he states he actually paid more than required % during the years prior to his disabilty claim. We have no way to verify this unless he provides proof. Again, let me stress, he is EXTREMELY verbally aggressive, vulgar, and paranoid in his thinking. Talking with him is not an option that he will allow or we want to encourage. His current spouse is not a viable contact point.
My questions are: How can visitation continue without being assaulted by him at the point of exchange?
Can he actually claim reimbursement from me for his voluntary overpayment of CS, IF that is in fact true?
Help! Thanks!

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