Vodacom not cancelling contracts like requested

I cancelled my contract with Vodacom in Sept which they told me the last payment for this contract will go off on the 1st of Nov 2017 only to find out in Dec they still have not cancelled the contract and they still charging me for the contract I then phoned them for a second time to cancel the contract on the 7th of Dec which they then told me it's cancelled. They took the data away for this contract and said they will refund me for the money taken. On the 12th of Dec I phoned again to make sure the contract is cancelled which they are charging me again on the 2nd of Jan 2018 for and I got told it's on prepaid and I told them I don't want it anymore. Don't know anymore how to sort this out with Vodacom and then they want to ask me why I don't want to upgrade my contracts with them