Had a similar issue not long ago, garage whacked the air gun on and broke the locking wheel nut and then said the bolts had seized in and it was not a fault of theirs - claimed they had the breaker bar on it not the gun. Also said 'we can try to hammer a socked on it but it may damage the alloy so dont want to do that' wasnt until later I spotted they had tried exactly that and you could see the chips in the alloys. Normally a good place but must have had a newbie on it that day!
Took the car to my mechanics with new locking nut, used the breaker bar and eye presto, no issues. He said straight away, they have used the gun on this to cause this damage.
Wasn't pointless trying to stand and argue the toss, nut was £10 from the dealers and they had all their excuses lined up.