Deductions for a product that was not delivered.

I had a data contract which was ending in February 2020. I received a call from mtn for an upgrade and i agreed to extend the contract. The product was not delivered. I tried calling mtn to make follow-up without success. I decided to send them an email to let them know and also cancel the contract because they took a long time to deliver. In May Mtn started to deduct money from my account. Mtn has been deducting money from my account for a product that was not delivered, when calling them they say that they are changing systems the cancellation was logged on the 15 June 2020. I need assistance to cancel this contract and get a refund. 8 months is a long time and money. I have been calling for feedback every month.