Incorrect billing and no one to assistance

Vodacom has been billing me for a SIM card which was initially a buy one get one free. When the contract ended I called to cancel said sim and was told there was no need it will be moved to prepaid. I later noticed I was been billed for the SIM card and called to get this resolved as I am not even using the SIM card. The guy I talked to was not listening instead wanted to sell other products which I told him I was not interested. I sent an email to request that the sim be cancelled and there was no response. This month I am billed double on the said SIM card. I believe Vodacom is a **** trying to gain money from their clients.