MTN Cancellation of contract

My contract with MTN expired in June 2020. I've been trying to cancel this contract with them ever since. No one in any of the MTN stores in Menlyn would assist me with the cancellation of this contract and insist that I call a number where nobody answers even after being on the line for 1h20 minutes or more. They continue debiting my account every month so the only conclusion I can draw is that they want to ensure that you are not able to cancel your contract!