<prompt> Human: I have an old checking account with a major nationwide bank that ended very poorly. Between fees and overdraft charges it was in the neighborhood of -900. NONE of that 900 is a bad check. It is just the fees and misc that the bank charged me. This account was closed in 2006 and charged off as uncollectable in 2007. I have been receiving some pretty aggressive phone calls from a collection agency demanding I pay this money. The issue is, I dont have 900 and they are also telling me that they have been charging me interest on the balance so now I owe 2500. They refuse to send me any paperwork detailing how the interest was calculated. They just say thats the way it is. Is it legal for them to tack on an arbitrary interest rate like that? Was that info in the small print on the checking account paperwork I signed?I know if I make even a small payment I accept the fact that I owe the debt and the clock starts ticking again for it being on my credit report. Basically any info would be appreciated. ps. I live in Iowa. Both now, and when the account was active.  <response>: Dispute the debt, but do not make a payment or admit you owe the debt. If you send them a formal letter, they are required to send proof. Some help for the letter:FYI, they cant charge interest or fees beyond what is in the original contract you have with the bank and Iowa state law. 