Collections Hassles

My father has a car loan with Wesbank and has made late payments due to the economic climate. He is settling these and payment was made using FNB which is a subsidiary of Wesbank so logic would dictate that their systems are linked. But NO they are not. So I email the statement to confirm that the money was deducted. However, he is still being contacted by their collections department who couldn't bother to check the emails to confirm that the POP was sent or trace the debit order.