My question is, what is the correct response? I have currently just informed my accounting firm about their mistake.
My personal view, people often expect perfection until it is their own mistake, I wish people would give others (including companies) the same benefit of the doubt they'd like to receive when they make a mistake. Not saying you aren't but assuming they at least apologized and said they have addressed it I don't think there is any reason to do anything else. Of course, if you know this company is sloppy, first why would you use them, but second then it is more fair to raise this issue more publicly. But unless you want your every mistake judged the harshest way possible, I say accept people (who work in companies) will make honest mistakes, address it with them and move on unless it is chronic or abusive.