Debiting Account After Contract Has Been Cancelled

I cancelled my Cell C account and paid the lump some to do so in September 2014.<br> Since then, Cell C have continued to debit my account for the past 6 months, including adding charges for a number I have never owned. The total undue debited amounts to +-R4200.00.<br> I have made contact with Cell C through written correspondance and the customer service call centres to get this resolved. The call centres give the same excuses, such as \the supervisor is unavailable"and \""we have referred your query to the retentions department and someone will call you back within 24 hours\"". Needless to say"