contract cancellation

In Aug 2015 I called Mtn customer services to cancel a contract I have as I'm not working and I cant b able to pay it every month so I wanted to settle it, the agent gave me a settlement balance of which I paid the very same month ref nr ***. In Sept I get airtime then I call again to ask why m I getting airtime coz I cancelled the contract, he tells it's a mistake not urs bt ours bcoz I Can c thrs a cancellation on the acc I Will send it again to the person in charge and they wil sort it out. Ref ***. In october same thing happens again ref *** I call them and the story changes the money that I thought it was a settlement balance its for the monthly fees and I was surprised coz I wanted cancellation of the contract. I also wanna know how does it take to cancel a contract with mtn coz I can see you dnt care abt customers. Your service is very disappointing. I'm feeling annoyed because of this