Go back to the court where the custody & support order were. Ask wehre you can find forms to fill out to change custody and support. File them NOW. The court might not get to it right away, but when they do, they'll go back to the day you filed (or actually, probably, the month after the day you file) when they finally get around to looking at your requests, but if you don't file them, it'll never get done & you'll still owe support until it's all official with the court.

The clerk of court should have a handle on where people representing themselves can find the forms for this, becasue it's quite common.