FNB Loan Installment

I have a loan with FNB, of which I have NEVER missed an installment. The installment date is set for the 30th/31st of each month. To my suprise, the installment was already deducted today (19 December). I didn't receive any kind of notification from FNB, notifying me that the installment would be deducted earlier. How can they just take the money that you didn't make provision for at this time AND who is going to pay the bank penalty fee for not having enough in your account? Very disappointed in how FNB is doing things.