They continue to over charge me without solution

I complained here a month ago about African bank that kept on over billing,charged arrears interests and a lot of insurances that I don't know where they came from, someone from collections department called me and acknowledged the mistake they made as she saw them,the told me she is handing over the case to some department that will investigate the matter until today they haven't solved anything,it's worse because now last week Thursday I paid off my other account that was left with R107 that they still over charged, they tell me that they don't see the payment. It's over a week after I made that payment I even sent them a proof of payment several times but only to find out today that they ignored the payment I made and increased the amount again, on the account that I paid off already. I'm really ****ed off if this the way the treat their customers or make its highly not acceptable and I regret everything about them especially their bad customer service that sucks.