What documents can I send to the ex that would terminate his claim on my son?

My ex-husband agreed to pay a set amount of support before leaving the home. Since that time, a protection order prevented him from contact with myself and the kids. As a result, he has contested support formally twice, and owes over $2,000 in judgment. My special needs child is very well cared for by my fiancé. Although there is a protection order, he still has the right to information regarding education and medical care, along with supervised visits. He has declined all of that.