Lines billed to wrong account - no refund

We had lines billed incorrectly to our account - after sending numerous Emails we still have not resolved this issue. It was suggested that we get the money back from the other client ourselves - this was an error by MTN and should be refunded by MTN surely?<br> <br> Can someone in a senior position please resolve this, because we have not had any response from Stanley Makhubu, Khosi Mbatha and Cathy Botha.