MTN continues to debit money out of my account despite me canceling the service

I had a 24 month contract with MTN from June 2018. I cancelled my contract in September 2020 when my contract ended in June 2020. MTN continues debit money out of my account despite my and my banks request to cancel the entire contract and I don't understand why. I've done numerous debit reversals but they continue to debit the money out of my account. I'm very disappointed with their service and I will not work with MTN in the future.