MTN still debiting months after contract ends

My mother has been trying to cancel her MTN contract since it ended in March 2022. They have been taking money from her account every month despite numerous attempts to have it cancelled, we went to MTN stores but still, they give us the phone to talk to other people, who hang up on us upon hearing that we want to cancel the contract. The cellphone numbers that came with the contract have been blocked so it baffles us why they are still debiting. What should we do to get MTN to stop taking our mother's money. This is very disappointing.