Rear differential making noise and metal shavings in the fluid?

My truck was parked on side of the road and was struck from behind.
Bumper left side of bed, axel slightly bent, left rear tire and rim damaged. Got those items repaired or replaced. Drove it 5,000 miles and the rear differential started making terrible noise. Opened drain plug, lots of metal shavings on plug and in the oil. The insurance company claimed that the shop did not install axles correctly and that is the cause of the differential failing. I asked what evidence they have if that being the case and the adjuster said she didn’t have any evidence but that is the insurance company’s position.