Standard Bank
Credit Card payments not recognised

I have a Credit card which I mainly use for buying camping equipment for holidays and when I use it I almost immediately settle the entire amount. My primary bank is ABSA and I do monthly EFT payments to Standard Bank. This procedure has been going on for at least 10 years. Now, after all these years I received a letter for arrear payments and a threat to report me to the credit bureau. When I called Standard Bank they said that the account I was paying into does not exist. So, how can I make payments for such a long time and never before received a notification of arrear payments.