MTN Customer Service is atrocious; I NEED HELP!

MTN keeps cutting my mother's line (on a daily basis) saying that she owes you money for a contract she terminated in Aug. Now you want to force her to sign a repayment plan? How is this fair? She is being held hostage. NO ONE has been able to assist; stating that "computer says no". This is ridiculous. She has been a loyal customer for decades yet you treat an old frail woman like this? I NEED HELP PLEASE! No one is responding to my emails. No one assists when we phone Customer Service. HELP ME!!!!!