Nedbank deducts without permission

my name is Janice R Adams. I currently have an account with Nedbank MFC account number ***. I was in arrears of an amount of R2084.51 which is not even for a full installment. MFC, without an arrangement have deducted an amount of R1627.54 resulting in my account being in the negative. I am requesting that this amount be reversed due to the fact that thewy did not inform me of this and do not have the right to just deduct without my permission based on the fact that i also bank with Nedbank. Please can someone assist as not following due process. thank You