FNB exctremely bad service / no response

Okay so another month has passed with still no response from FNB regarding the account that I have been paying for over a decade without missing a single payment, interest again added and I owe more than double that I borrowed in the beginning, then to top it of the company 'Capital data' sends me reminders that I have been handed over to them for this debt to be paid and my ICT score gets affected by FNB who just does not care about their customers. This is by far the worst service imaginable from a bank and then prides themselves in customer service and if it was just a few bucks it would have not made such a big difference but it is a massive amount