Legal Question in Family Law in Montana

"I agreed to forgive ...": With whom did you agree?

If it was in court, and it resulted in an amended child support order requiring the lump sum payment, you can file a Motion to Enforce Judgment of the order. Don't forget to ask for interest on the unpaid balance. Yes, you can request that payment revert to its previous method. The court might agree if control over the previous method is through income withholding.

If it was a personal agreement between the parents, and you have a signed agreement, you might have success if you file a Motion to Enforce with the court. If it was an oral agreement with the obligor, then "it's only as good as the paper it's printed on." In court, you'll say we had an agreement, the obligor will say no, we didn't. You need to be prepared with proof, e.g., any letters between you that talked about the amendment, anyone who was a witness to the conversation, etc.