Failure to cancel contract after numerous requests

I app**** for a new contract with Vodacom on 27 June 2015 at Vodacom The Grove. Vodacom sent a cancellation request to MTN. On the same day I received 2 sms' from MTN confirming that they receive a request for cancellation and should I not reply to this sms the contract will be cancelled. I did not reply and later received the 2nd sms confirming that my contract has been cancelled. However, MTN has debited my account for the monthly subscription in July and August and I received and account for September as well. I phone the customer service and asked that this be corrected but they can just confirm the account has not been terminated and can do nothing more. Each time they say that they will send a request but nothing has happened. Every time I phone it is as if nobody knows of any previous calls from me regarding this matter which indicates that the calls are not recorded. When I ask to speak to someone more senior I just get put on hold.