Cancelled a contract with MTN but still charged

I signed a 24 months contract with MTN that ended 30th of August 2017 , I called MTN to cancel my contract and also want to the shop(Maude Sandton) my contract was not cancelled I was told I need to write go to 14th Ave MTN head office since they don't cancel contract. when I called all the calls were recorded and the recording is there that I called cancelling my contract. imagine staying in Taung having to travel to 14th ave to cancel a contract.