Your going to be fine, at least the problem was fixed without lawyers getting involved.
You just need to match the firewall material , which most likely is some 5/8 sheetrock. Not a big job at all, and probably nothing you have to rush out and do today.
Then, talk to the cotractor to fix the wall, and be polite, it gets things done easier. Nothing sends em running faster than someone livid and fumming.
Send us the picture if you can, we give better advice that way.