Failed Cancellation AGAIN

On the 11th December 14 I went into Cell C in Grand Arena Centre in Cape Town to inform them that I was not extending / renewing my data contract and it was confirmed that it would not be renewed and my last debit of R118.98 would be December 14. I was then billed R264.16 in January and so I phoned to query this on 2nd Feb 15 and I was told the contract was not cancelled and I was paying more than double because all discounts were no longer applicable. I then spent 45 minutes on the phone trying to get a refund and eventually from sheer frustration I gave up on trying to get that money back and asked the agent to cancel my contract immediately. I was told there was 30 day waiting period and it would be cancelled as at 31 Jan 15. Well this too has been a complete waste of time as you have now debited R279 for February and this is tantamount to theft. Please advise as to what one must do in order to cancel a contract if one cannot do this in person or by telephone?