It sounds like there was a bill with a balance at the time you filed the nonsuit. The Amicus would have to sign the Non Suit before the judge will sign it. Either pay the amicus or work out a payment plan with the amicus and then ask the amicus to sign the nonsuit. Then the judge will sign it. If you and your ex had attorneys, ask the attorneys to handle this matter.
I recommend that you consult with an attorney regarding this matter.