attempt to cancel contract.

I visited Mokopane MTN store to enquire about cancelling of contract and migrading to prepaid,the sales consultant advised me to do it in writting.On the 15th September i went to MTN Mokopane branch to submit the letter,upon arrival the same consultant said i should rather call customer service because cancelation is done immediately.I then called 808 customer service.The consulted then told me to write a letter to retentions requesting for cancelation.He said to me they will then contact me within 24 hours.I was not contacted as the consulted said i would,i then called 808 again.The consultant who assisted me this time said i was not suppose to sent the email,because its done by them(consultants).I was really confussed because the previous consultant spelled retentions@ mtn word for word so i dont mis-spel the address.She then assured me that she will log a request for cancellation.I have been given 2 reference numbers which have not helped me in any way in the 4 times that i called in now.i have now received airtime again meaning i will still be debited on the 15 of November.No one can give me an explanation,they keep on promising while they take my money from me.Please help