If you don't have anything in writing, you may be out of luck. Although if he makes more than you at this point, you can request to go back and have child support re-evaluated. It's a percentage based on how much you make. If he's threatening you, all he can do is threaten. Once you're in court, you can tell the judge and show proof that he's "forgiven" all previous payments. He will have egg on his face and he's just trying to use it as ammo. No judge will award full custody to a parent just because. Most likely he's just trying to scare you into letting him get what he wants. I have an ex like that also. Just refuse to discuss it with him and tell him you'll be happy to see him in court. He may back down, he may not. Either way, he'll have to prove you're an unfit parent and I doubt you are. Good luck!