Cell c please cancel my account that is going to far to long now

I got a settlement letter from cell c stating that if I pay the full amount my contract will be cancelled ( 4,months back) last month I got a debit from cellc I went to the shop at waterfall mall in Rustenburg were I ask why is my account debited I was told that I have a month to month contract I have not signed anything with cell c for the month to month I don't what anything to do with cell c I have been calling trying to cancel the contract I cannot get answers I pay for service that I'm not using I have it in writing that if I pay the settlement they will cancel my account please advise if they is another way to stop all this