Contract cancellation dispute

I called MTN on 26/09/2022 to cancel the contract that was ending 23/10/2022, after emailing on 23/09/2022 and not getting a response. I was told that the contract will end on 26/10/2022 because of the month's notice required. However, the contract was not cancelled on the agreed upon date and I have been billed for it. I called again on the 21st of November 2022 and was sent from pillar to post with no one taking responsibility for the error. The retention and billing consultants I spoke to all agree that my request was never initiated/processed as requested, but somehow I am liable for their incompetence.