Debit Order Mandates are ************* from FNB

I recently app**** for a loan and as all debit orders you have to accept a mandate from the bank which we both agree on a preferred debit date. My chosen date was the 25th and the mandate specified the 25th. But to my surprise I am being debited every month on the 17th, this is the second that I have experienced this and when I called to query the consultants say that I apparently accepted the 17th. I do not understand why I have a mandate stating the 25th but FNB records have another date. I was additionally advised that it will take 5 to 7 days for the reversal which now affects my finances and the FNB consultant then advises me that I will have to pay extra for them to change my debit order date. This is all due to poor service received during the application but I am paying the price for it.