Rewire, I got hit with a similar "invisible" bill for a hole that was poked through the roof in a brand-new 10-story office building. They swore that we drilled through the roof decking, through 2" of Styrofoam, 2" of other "whatever", then the rubber membrane, the tar, gobbledy-goop, rocks and what have you.
There were crazy rains and the flood damage was absolutely unbelievable throughout the building.
We proved that we were simply shooting sheet metal screws into the roof decking on the bottoms of the corrugations, which is perfectly acceptable. It turned out that the alarm contractor had been using a 1/2" SDS hammer drill on each floor for their mountings and they forgot that they had reached the top level.
We had to pay a huge amount of money in legal fees to defend ourselves (paid by the insurance company fortunately), but in the end, it was proven that the other contractor was the culprit. They had drilled the hole and just packed it with Duxseal within six inches of one of our attachments.
Stick to your guns and demand details. I'm sure that the cost of this bill is equal or less than your insurance deductible, but sometimes you need to waste the money just to prove a point.
