Credit card

I have been a client with nedbank for as long as I can remember about 7 years ago I had a credit card with them. I used it for about a year then paid and closed the account. About a year later the balance went from o to R400 and something I kept trying to cancel instore and over the phone. They said its closed and cancelled. Now so many years later I keep getting hounded about a balance of R580 I called again they said its cancelled. Still SMS everyday. I feel disgusted and unhappy because now it is affecting my credit score. I will not pay the R580 as I have never used the card since 2012. I want to be reimbursed and I want it closed immediately.