Do you have a one of those bigger carpenter squares ? If not borrow one. Take it with you. Have them show you it AND the bolts that hold it on, were not damaged.
Remind the insurance company about their potential liability and if that if the hitch is still square and undamaged, that you would like the bolts to be replaced.
Even though it sounds like the hitch didn't suffer any impact damage, the bolts themselves could have suffered inertia damage and could have been stretched.
Just my opinion.