Cancelled account

I have tried to move my account to prepaid since may 2017. Have spoken to agents and even chatted online with an agent who all promised to move my mobile account to prepaid. Ironically i need this done to get off a voice contract to move to a data contract. I have mailed 3 different people directly as well as the cancellations department, but no response, all the while charging me monthly. It is now September and still i am being charged. Can someone at Telkom help with this?