MFC breaking contract - debit order date

I have debit order date for the 25th of each month. In November MFC changed it due to some Campaign and changed my debit order to 22 November 2025, due to some customers which want it to be deducted earlier. I am not one of them. I cannot understand how MFC can change the debit order date which was agreed to on a legally signed document. I now get messages from my bank indicating insufficient funds. This is unacceptable, if customers want to have their payments go of earlier then they can phone MFC to do so but MFC do not have the right to change my debit order date.