Worst service - we expect more!

I am acting on behalf of Abrie Marais who is no longer residing in South Africa since September 2015. (I have a Power of Attorney). Abrie attempted on numerous occasions to cancel his MTN contract as he relocated to England and he attempted every possible manner to do so by going into an MTN branch, phoning and sending e-mails. However he only received empty promises and MTN never cancelled the agreement or gave him sufficient feedback. Since he relocated, MTN proceeded to deduct money from his SA account by debit order, he by the way cancelled each debit order. Please let me know what we need to do to stop MTN from deducting the money from his account and to cancel the agreement. PLEASE NOTE we will not pay for the account after the request to cancel was given in July 2015 already. Please urgently give me feedback, I have all the necessary correspondence to prove the attempts. We really expect more from MTN's service. Get your act together.