Mark Twain once supposedly said that "A verbal agreement is not worth the paper isn't written on". Without a written contract, there is no way to define the terms of what the creditor agreed to even of that admit to agreeing to the payment plan. You didn't say what the specifics were for the plan.
You are being sued for nonpayment of a debt. Perhaps the creditor wants the terms of the payment plan confirmed in writing before a court. Perhaps the reneged or really didn't agree. What you need to do now is see a local attorney who does debt settlement or bankruptcy to see about what your rights are now.
First, the firm is a debt relief agency according to the U.S. Bankruptcy Code. We help people file for bankruptcy. We also do other stuff and we do it well, but Congress wants me to post this notice. Second, nothing on this site is legal advice. You are not my client unless you enter into a written agreement signed by you and me.
Option one-Defend yourself in court with evidence that they agreed to a plan and agreed not to sue you. Your claim without evidence will not likely be sufficient.
Option two- ignore the warrant in debt, lose and plaintiff wins judgment against you.
Option 3- hire debt collection attorney to defend you. There are ways to beat the debt collectors.
NOT LEGAL ADVICE. FOR EDUCATION AND INFORMATION ONLY. Mr. Rafter is licensed to practice in the Commonwealth of Virginia and the US Federal Courts in Virginia. There is no implied or actual attorney-client relationship arising from this education exchange. You should speak with an attorney licensed in your state, to whom you have provided all the facts before you take steps that may impact your legal rights. Mr. Rafter is under no obligation to answer subsequent emails or phone calls related to this matter.