MTN doesn't or can't cancel a contract

I've been trying to cancel an MTN cell phone contract since 5 May 2023. I notified MTN, I paid the penalty amount MTN asked for, but they are still billing me. I've called, emailed and have been physically at their customer care center at MTN's head office twice. They are still billing me. When you call them they send you from one department to the next (back and forth between the Billing department and the Retentions department) Emails are answered by what seems like a machine as the reply is not relevant to the issue/problem. If one sends an email to a supervisor, another person responds. How does one get MTN to cancel a contract as they DO NOT want to do it.