Debit account on unauthorized date

I have an arrangement with MBD credit solution for my Woolworth credit card. The agreement is that they will debit the agreed upon funds from my account on the last day of the month. Now they have put a track on my account which they refuse to remove. I have not agreed to have funds taken from my account on any other day but the last day of the month. This deems these debit order unauthorized!!!!! Remove that tracker from my account or I am cancelling your debit order PERIOD!!!!!