Unhappy Wesbank Client

I recently bought a car and it's been financed with Wesbank. But I realised that for the past two months debit orders weren't going off on the correct day of the month. I had to call and find out what was wrong and they explained that the account details weren't loaded correctly and this was only resolved yesterday. But now even though they admitting to have loaded the details incorrectly they still want to go ahead and charge me interest for Debit orders not going off on time instead of reversing the charges because it was their fault that the account was not paid on time and not mine