Chubb auto insurance-they screwed me!

When the other car went through a red light and struck my car, i thought this would be a no brainer. Then, Chubb became involved because the other guy had Chubb and I have Allstate. The Chubb appraiser evaluated the damages to my car in a parking lot in the rain while I was not present. He determined that about 1/2 of the damages were already there. I tried to straighten this out on the phone with their adjuster but she hung up the phone on me. Then, her supervisor wouldn't return my calls. Now, they have sent a check for only 1/2 the damages.
I am sending the check back and now running the claim through my own insurance policy with a 500 deductible.