collection letter for 1989 debt from Assett

If someone can help me with this. I was rather surprised when I received a letter yesterday from Financial Recovery Services for a debt of $500. My credit is good (I just received all my credit reports and did not see any bad debts or collection items) Called the number and the person said they were a division of Asset Acceptance. Could give me no info on the debt which is from a company called Ameristar Financial. They said it was from 1989 and I should send in a letter requesting more information. While searching for info on Asset, I stumbled on to this web site. Looking at some of the postings, it has made me rather nervous to deal with this company. I reside in MASS, however, if this debt is legit, I was a resident of FL in 89.
Can I have your recommendations on how to proceed from here..much, much thanks.