Advance American Load

I took out a payday loan 2 years ago from Advance America in Michigan. I was not able to repay when time came and was paying in small installments, then defaulted. Several months passed, and I occasionally was able to make a payment but still owed about $500. One year after the loan the company walked over a "copy" of my check (not the original) and presented it to my bank for payment. The girl honored this, even with the date being a year old. After I questioned this, they contacted Advance America and told them they would reverse this, since it was over a year old. Again, I made a couple more small payments; then the manager was either fired or quit. I didn't hear for some time, then a few months ago I talked to a new manager there who was trying to clean up some outstanding loans. I told her than I had made payments on it, but they did not show this (she speculated a bit on the past manager's record keeping). I was told they would get back to me on the matter, and I waited to hear. Now I have had two or three calls from someone saying they represent the bank for this company who loaned the company and he is threatening legal action. I have gone through all my saved receipts but not able to find any of the payments I made - probably tossed away over time. What are my options here??