Capitec cruelty

I bank with Capitec. 15years ago l had unpaid account with Capitec which was written off. The amount was R3000. When trying to make payment l was told that the account was written off as a result l am unable to make payment. Evertime l visit Capitec the official will tell me of that 15 year old mistake as it is the first thing appear when accessing my account. They told me that it remains permanent on my record. They refuse me to pay and remove. What can l do ? What kind of a bank that blacklist customers for life who are willing to settle the account ? Is this a bank or loan shark ?