Debt accumulating for non-existent membership.

I tried to sign up for membership earlier this year and was told I could not sign up because of an outstanding debt of 2012 for an account membership that I had closed, owing nothing. For the past couple of months they have been hounding me with calls and emails. With each call I take the time to explain the problem and they promise to look into it and get back to me. But instead I get calls and emails again demanding that I make payment for my current membership. This being the membership that could not be approved because of historic amount that I have no knowledge of. So it seems now they are accumulating another debt based on the most recent application that was done but declined.