DEBIT ORDER

During January 2015, I lodged a complaint with MTN (ref: MTN REQ:***.) that monies was deducted from my bank account. (I never signed a debit order to effect this) I have a contract that is paid by the National Department of Human Settlements. Upon further investigation MTN Sunnypark acknowledged this error and the Manager tried to assist. However, Nedbank, how do you instate a debit order without the consent of the client. Now neither MNT nor Nedbank are able to re-reimburse me??? Nedbank, please assist.