MTN making ******** upgrades and taking money without permission

My husband was upgraded WITHOUT his permission 4 months ago. The new contract was double the amount which they began debiting from his account, again without permission. He has called numerous times, disputing this upgrade. MTN cannot provide any proof that the upgrade was agreed on. They promised that the problem would be resolved and he would be refunded. It has NOT been resolved and he’s basically being ****** by MTN for 4 months now. As a last resort he stopped the debit order and MTN has now discounted his contract and have left him unable to use his phone which is unacceptable.