Mtn not cancelling contract as promised

My fiance went into the Howick branch to cancel his contract on the 17th of December, the consultant said it would take 5 working days to cancel and change to prepaid (the contract is past 24 months). On the 20th, it was loaded again with the data and credit, even though he had cancelled it, and spoke to a consultant on the 23rd as it still wasn't changed to prepaid. She said her supervisor would be in contact but did not ever respond. When he phoned again on the 28th he was told that it was not logged on the system on the 17th, only from his call on the 23rd so he must wait another 5 working days (so by 30th December it would be cancelled). It is now the 1st of January, 11 working days later, and it still has not been processed!! How must he cancel his account??