You can file a Motion for an Audit of your case in what you have paid out if the Judge finds you over paid and no back child support is owed and you keep your child support current you can either request credit for the overpayment or you could get the monies back just depends on the laws of the state you live in
You must contact the court which set up the child support order....the best to you
It's a long process but take all payments you made to show how much you should pay and see if that will help. Good luck
If you paid via the government then contact that department and state your case.