Been paying on loan for six months and being sued by law firm now! Help!?

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I'd fallen quite behind on payments last year on an old school loan. I'd been contacted by both a law firm who were really mean, nasty people, unwilling to work with me at all. At the same time, I was contacted by a collection agency on the same loan, was told I could make payment arrangements and have done so for the last six months. I never heard again from the law firm until now, when I've received a legal form "entry of default" from a local courthouse. In contacting the original lender, they have no idea who the law firm is, and show record of payment for the last six months. When I called to the law firm, they laughed at my payment arrangements, and said they'd see me in court, despite the fact that they're representing a company who has told me they don't have a law firm involved.

Any thoughts on what's happened? What do I do?

Also, the collection company I've been making payments to has no idea who this law firm is either!