Unauthorised double debit order

Personal loan debit order deducted on 27/11/2018 and on 14/12/2018 instead of at the end of December as suppose to. I was not notified of this and did not give any consent for the second deduction to go off so soon. I tried calling FNB on Saturday the 15/12/2018, no answer and I wasted R40 airtime. Tried again this morning but once again no answer or after making a selection from the menu, the call gets cut. This is not fair, especially before this festive season to double deduct someone's account. Can someone please call me to have this matter resolved.