Contract cancelled but still being debited

I contacted MTN in 2009 to cancel my contract as it had expired and they promised me that it would be done, however the next month i was debited again and when i called the call centre again to find out what the problem was they mentioned that it does take time and will be cancelled shortly and i will be refunded. However the next month again i was billed and when i called to query this the agent mentioned that it is becuase it is a corporate contract hence the delay in cancellation. This went on for another three months until the agent advised me that i must not worry as they will definetly cancel the contract and i will be refunded. Up to this day i have still being paying this contract and when i contact MTN now they say they have no record of me calling them!! i am highly upset at the lack of service that MTN now provides and the fact that they debit my account on a contract that i cancelled with them years ago and still have the nerve to say they have no records of me calling them in 2009 and 2010.