Telkom poor service

Cancelled my service on 19 March 2018. Got a confirmation that the service will be terminated 21 workdays after that date. Received an invoice at the end of April for the full amount and then again at the end of May. I logged a dispute with them but still receive statements with interest on the outstanding amount. I again went to the customer service last Friday with the promise that I will hear from them in 48 hours..... Still waiting. Very POOR service.