Terrible service by VW Finance

I called to move my debit order date as they had made it the day my salary gets paid in. The lady said I could choose any date so I chose 29. She asked me if I am sure as she won’t be able to change it back so I said I’m happy with that date. Once she made the change she gives me a new installment amount , so I ask if the change is because of the interest rate and she replies no it’s because you moved the date up . So I say surely you should have told me the installment would change before you changed it , so i tell her in that case you can leave it on the 25th because I’m not prepared to pay interest on the four extra days for the next 5 years . She then says it can’t be changed back. So now i have to pay an extra R720 on my contract for moving the debit order date which they refuse to change back . I am incredibly ****ed off as I wouldn’t have moved it if I had been told there would be a cost involved , I’ve sent 3 emails to complain that I was not informed about this over the phone and not one of my emails have been rep**** too. I feel cheated by this company and will never use them again for car finance in the future .