Insurance denying part of claim

I was hit in a fairly low-speed offset frontal crash (their front driver side hit my driver side), combined speed maybe 20MPH. Other party fully at fault and insurance covered it. After 5 weeks in the body shop I take it out for a drive just to make sure everything's good. But now the car vibrates once you get close to 70MPH. This vibrating did not happen prior to the crash and nothing was noticeable when dropping the car off at the bodyshop (it was still drivable)

Insurance adjuster then reviews it with a mechanic (mech said I have a bent axle) and the adjuster is saying their stance on it is the bent axle is caused by wear and tear and they're denying the claim. Unless I can somehow get a VW mechanic to lay out how a head on crash can bend the axle in this specific car.

What are my options here? Everything I've read says that wear and tear does not bend an axle, only impacts like collisions, hitting a curb hard, or a bad enough pothole. It seems like a ridiculous hoop to have to jump through, to get a VW certified mechanic to specifically say that yes a collision can cause a bent axle.