Cell c trying to rob me

I had a month to month contract with cell c since last year then I decided to cancel it this year I called them sent emails then finally the contract was canceled but the issue now is they want to keep taking money from my bank account every month while the contract is canceled, I took steps and called again to address this with no help from cell c staff they kept on telling me they don't know why my account is debited I have spent hours on this trying to resolve it with no assistance now all of a sudden they call me threatening to blacklist me what a nerve people stay away from cell c they are extremely unprofessional and will try to ***** you out of your money