Impossible to change my Standard Bank vehicle finance debit order date!

Since I bought my 2016 Chevrolet Utility through Standard Bank Vehicle and Asset Finance a year ago, I have been asking at them to change the debit order date of my monthly lease agreement installment from the 25th of each month to the 1st. I have called at least four times about this before. I have sworn and screamed and begged and pleaded, and today, once again I discover that this has STILL not been done! Not only that, but the supervisor had the absolute temerity to ask me to produce the reference numbers of the previous calls I have made, since they have NO RECORD on any of the calls on their system! I do not get always paid exactly on the 25th. I can receive my salary anywhere from the 25th to the 1st. Whenever a Standard Bank vehicle finance debit order bounces, Standard Bank REFUSES to change the debit date, because the account is in arrears. They will entertain a discussion about changing the debit order only once the arrears have been cleared. And of course, to add insult to injury, they charge my interest on the arrears each time, and send me insulting SMS notifications informing me that I have to call them immediately to fix the issue! AGAIN! And this keeps happening over and over and over, and every time, I am forced to spend half an hour on the phone again, begging them to change my debit order date! Which sick, demented sadomasochistic freak invented this disgustingly ineffective internal process?!