Debit order coming off on earlier dates than agreed

After logging a number of complaints previously over the past year this issue is still continuing. I have 3 debits orders with Standard bank 2 loans and 1 vehicle finance but almost every month the debits orders are coming off on the 22nd or 23rd instead of the agreed upon date of the 25th which is in the contract signed. The excuse of the 25th falls on a Sunday is completely invalid as the vehicle finance debit order doesn't come off only the debit orders for the 2 loans. This is completely pathetic service from Standard bank as this is causing me to pay additional banking fees for my account being in arrears.