I'm very disappointed because MTN keeps on deducting money from my mother's bank account after the contract expired

I'm very disappointed because MTN keeps on deducting money from my mother's bank account after the contract expired. We've went to one of their stores for a few times, asked to cancel the contract, but we experience the same problem every month. They refuse to cancel and keeps on calling for an upgrade. They also don't want to pay back the money and has alot of things to say. We've only received the R220 of this month after reporting them here at Hellopeter.