Mtn deductions

I had a data contract which was ending in February. I received a call from mtn for an upgrade agreed to extend the contract. The product to be delivered in March but it 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 along 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 I have calling them they say that they are changing systems the cancellation was logged ion the 15 June 2020. I need assistance to cancel this contract and get a refund. 3 months is a long time to be giving a system change excuse.