Cancellation of contract

After reaching the end of my contract period, Telkom informed me that I must fill in a form to cancel my contract, as this does not happen by itself. So on 27 November, I have sent them the cancellation form. It has been a full month now, and I have not even received a confirmation that my contract is cancelled. When I phone their helpdesk, the call agent just says that my contract is still not cancelled. Meanwhile, I am still being debited for something that I do not even use.