We have no way to investigate this - what may have happened in the last 20 - 30 years, or when. I suspect, though, that you are dealing with a junk debt buyer who recently acquired for pennies on the dollar the bad debts of the company you dealt with, and is now trying to collect them without regard to the statute of limitations. As I see it, your choices are to investigate to try to find out if the debt is valid, to assume that the debt is not valid and tell them to stop contacting you (for example), or to do nothing and see what happens.