Double debit

Nedbank MFC has really put me out of budget this Christmas. They normally debit my car installment on the 15th . This month I got paid on the 6 and I phoned them to make an arrangement that they debit me on the 7th. They did that. And I was told that the next debit will go off on the 15th of January as usual. To my surprise on the 15th of December I was debited again for my car installment. Because of this I have had my other policies calling to say there are no funds in that account. I phoned Nedbank and was told that the money will be reversed bank into my account but still they have not done that. This is going to be a black Xmas for my kids and family because of Nedbank MFC.