Cancellation of contract

I have a contract with Vodacom which was cancelled timeously on 17 January 2015. It is recorded on the system. However, the phone is still not on prepaid after contacting the cancellations department several times since 1 March 2015. The contract is in my moms name and we reside in different cities. My mother has actually taken the time to go into one of your contact centres and called cancellations again and was assured that the number would be on prepaid within 24 hours. Needless to say more than a week after that the number is still on contract. I ASSURE that we will NOT be billed for this month as it is not OUR MISTAKE. We have tried several times to rectify this without success. It is now up to Vodacom to correct this. Pathetic service, I will never recommend this provider to anyone!!!!!