Pathetic service from standard bank

I have an agreement with the bank to debit my account on the last day of the month, but for some reason they tried to debit on the 23rd and now I've incurred a penalty fee of R115 as if I'm the one to blame.This is absolutely ******* and such nonsense can't be tolerated, what was the reason for our agreement if they can debit me whenever they want? And who will pay that penalty fee? I tried to call and I hold for more than 30 minutes before I can get assistance and I get told to hold for another department.