Going to court may not be the worst option.
I am head over heels in debt, really I am bankrupt.
One of my creditors has brought a judgment against me for a medical bill of 5K. I have to go to court in a couple of weeks. I am in the process of making a list for the judge of all my debts and current payments. This includes a student loan in default which has grown from 35k to 43k since un/under employed; however, I do make very small payments on this loan (less than $50 a month although it grows by $300 a month because of interest. In court I intend to explain my state of bankruptcy to the judge and offer the creditor a small payment. There is no other option.
What I am trying to say is: If you go to court and explain what that agency did and ask to maintain your current payment plan, it may well work.
Also, what that agency did is called bait and switch. You were lured into a payback plan and then the terms were switched. I had a dentist doing this to me once. I had expensive dental work done and she agreed to a payment plan. The dentures were made and I still owed money. She did not want to release the denture and insisted on full payment. Luckily I was able to get a lawyer; It only took one visit. The lawyer wrote a letter to the dentist pointing out the “bait and switch”. The upshot: I got my dentures and did not have to pay the
balance. That dentist did not want legal trouble. There must be Federal agencies that deal with illegal collection practices, consumer protection agencies. You may want to contact your state attorney’s office to see what they have to offer re: consumer protection.