Still being billed for discontinued service

At the end of June 2015 the Telkom copper cables in my area were ****** for the umpteenth time and Telkom advised us that they would not replace the copper cables and we should switch to wireless. We duly did this and since then have been on wireless. Unfortunately I am still being billed for a service that was discontinued in July 2015 and this despite numerous calls to the Telkom accounts department and also filling in a cancellation form and sending this to them as well. Initially I was being passed credits for the incorrect billing, but the last 3 months bills have not reflected any credits, only charges for the discontinued service. I have phoned the billing department on numerous occasions asking for credit to be passed for the incorrect billing, but with absolutely no joy whatsoever. To date this discontinued service has NOT been cancelled and I have no faith whatsoever that the billing department to perform this simple task. They are TOTALLY *********** and cannot perform basic tasks. Is there someone at Telkom that can rectify this error and pass the requisite credit to my account? I have lost all confidence in Telkom and their ability to perform the most basic tasks.