MTN refusing to attend to debit order complaint

After my 2year contract ended, I stopped the debit order I had with MTN for data. They still went on and debited from my account. I went there to find out why and requesteded cancellation on email. They first said they would refer me to the right department but then they never responded to my follow ups. It's a second month now and they took money yet again, no responses. Calling has not been fruitful either as getting access to a consultant is difficult on their calling system.