Balance on account closed in 2015

In 2015 I paid a debt I had at Foschini and I therefore called to make sure that the payment was allocated correctly and account was closed. The lady I spoke to confirmed that the account was closed on their side. But after that the debt started from scratch accumulating and now I am being harassed by a collection agency that cannot even provide me with the statement of what I owe. Everytime they call me and I ask for the statement they ask me what is it that I want to do with the statement. This is really frustrating because I have paid what owed with Foschini over 2 years ago. I don't have an account with Foschini, please stop harassing me.