Vodacom does it again

Once again I have to do this for a company that does not listen to anything a customer says. I called in January to notify them that I will not be upgrading and would like to cancel my contract, which was agreed but instead they go and put the airtime in again for the month of March which is not supposed to happen. Now I am liable for the payment at the end of April whereas my last payment was march. When will vodacom actually know what to do and will they ever listen to their customer? I will never deal with them again. Someone better call me to fix this cause I am not leaving it here.