suburban mom

I was recently rear ended while sitting at a stop in my 2007 Chevrolet Suburban. When I picked up my truck after getting a new rear bumper and lift gate, the liftgate (not a power one) would not stay up by itself. I told the repairman that I had never had any type of issue of the liftgate staying up before the accident and felt that it should also have been repaired. He replied that there was no way that the accident could have caused any damage to the gas shocks. So I told him that then something must have been done during the repair because I think it is too coincidental that it worked fine before the accident and won't stay up at all now. Of course the insurance company is siding with the repair shop's opinion. Unfortunately, the insurance estimator never opened the liftgate because it was too damaged so I do not know for sure exactly when it stopped staying up. Any input you have would be appreciated. Is there no way the accident or repair could have damaged the struts? Thank you.