Telkom”s bad service

I am disgusted by Telkom’s service. I bought a SIM card from Telkom in June for the purposes of internet connection. I was told that should the SIM card not work as required, I would have the option of cancelling the contract and ceasing monthly payment. The SIM card did not work (and to this day I have not been able to use it), as a result I cancelled the contract via message to Telkom as reaching the telephonically has been impossible. Receipt of my message was acknowledged. However, Telkom continued to deduct the monthly payment from my account, regardless of my cancellation. I Would you kindly assist HellowPeter!