Premature car installment debit order

I received an sms from Standard bank informing me that my car installment would be going off on 21 Dec not the 31st and that it was for my convenience. I find it unacceptable that Standard bank describes its completely self serving act as convenient to me. How is it convenient for me to be put out of pocket for 10 days? When I called to refuse their offer I was left holding indefinitely by Thabang at vehicle finance. So can I please ask standard bank not to debit my account prematurely or I'll be forced to reverse payment which will put me further out of pocket.