credit card cancellation

I has a credit card with FNB and one day I got a message that owed on my card. I know I did not so I went into the branch and because the credit card department does not sit in the branch we had to call them. I was told my case was taken to debt collections. I asked why and the lady was rude to me screaming on the phone. The gentleman that was helping me at the branch then called collection department and I was told they do not understand why my account was even sent to them as they owed me money. I told him was very upset and the lady screamed at me like I did something wrong. I asked how much I needed to pay to settled then I transferred R1500. I asked him to cancel my card and he said it would take 7 days to be done. After 7 days when I went into my internet banking indeed my credit card was moved, not linked anymore. I took the card and destroyed the card. Now I am told there was no request from me to cancel my card but some how I automatically made changes and I still owe my credit card. It is clear to me that one day i will wake up and find that I am blacklisted by FNB For Something I AM NOT Aware Of.