MTN - battling to cancel and get refund

My mom in law has tried to cancel her data contract with Mtn that expired Dec 2022. She is 90 and has had to go into the branch every month . They keep telling her the contract is canceled yet They still deduct the money from bank account. She is awaiting for them to refund her 4 months and yet they can't seem to get it right. Every time she goes back the staff member dealing with it has left the company and has to submit all the documentation again. She has got to many reference number yet a reference number means nothing.