Bad service for refund

I received a paid up letter from nu-debt MTN but they continued to debit my *** twice after not owing them anything. On the 3rd September they escalated my request for a refund. Evrytime i call, the turnaround time changed from 7 to 14 to 21 working days. The last agent by the name of Thabile hung up the phone while I was following up. Its been a whole month since they said they will pay back my money. They bridged their own SLA. Im am very disappointed and would never recomend their service.