Cancelling MTN contract is a mission impossible

I signed a 36-month contract with MTN, which expires on June 11th 2026. I signed it at the New Market MTN store in Alberton. Every time I call a call center to cancel my contract, they try to persuade me to have a sim-only contract instead. When I tell them that I don't want a contract with MTN, they tell me that they can't do so because my number has been sanctioned. I call customer service, and they tell me that there is nothing wrong with my number—it's just an error on their end—and that the cancel department needs to escalate the matter and end my contract. MTN has not responded as of yet.