DEBIT ORDER DATE CHANGE

Recently purchased a vehicle that was financed through Nedbank MFC. The first payment was made in November and last week Friday the 13th December I received an SMS to notify me that they will change my debit order date to the 19th December to be in line with my salary date. This not possible as all documentation submitted and as per last month debit order this is set for the 27th of every month as per the agreement signed. So how can they change the date? is this legal? I did call on Tuesday due to Monday being a public holiday to confirm that the salary date is not the 19th and debit order should remain as 27th. Just received SMS notification from my bank indicating debit order transaction from MFC.