Changing debit order amount

So we all know the interest rate was increased by 25 basis points effective from the 24th of July - last week Friday. It is my understanding that interest in vehicle finance is charged daily - this was also confirmed to me by MFC's call centre.<br> However, my debit order went off on the 27th (3 days after the rate increase) but the amount was the new instalment based on the new interest rate. While the amount isn't a huge difference, why should I be charged interest back-dated to the beginning of July if the rate is only effective from the 24th? Like I said the amount isn't the issue but the principle. If I were to short pay my instalment by the same amount, MFC will eventually hand me over to their lawyers.<br> <br> Speaking about the amount, if MFC has say 1 million clients &amp