Been there, done that. If you have an agreement, he can’t ‘deny’ the claim. You issue a show cause for him breeching the agreement. You can make a claim for lawyers fees because he breeched the contract. He will have to answer the show cause in court. He will have to go to court and stand before the judge and tell them how not paying child support is not a breech in your contract.
If he is pissed that the support is too high, then he can try to modify if there is justifyable reasons, but if the agreement is only 2 years old, he may have to wait another year unless the reasons are justifyable to doing it now. If he SIGNED an agreement for an amount of money, then he is bound by that amount until a new agreement/order is created.
You do not owe him back monies because he feels he’s overpaid. My ex tried the same thing to the tune of 12K. He signed an agreement (dispite my asking ‘how are you going to do this’?), then got angry at ME when his ‘plan’ fell through for some job he thought he had.
I think he’s blowing smoke on the restitution. Unless you get formal papers from a lawyer, then don’t worry. I would issue a Show Cause for Breach of Contract.
He can still see his children dispite the arrears in Child Support.