(Bumper) Rear reinforcement bar

. I don't comprehend how geico can subtract 2k from my claim due to a reinforcement bar. Everything in the rear is managed BUT that safety bumper bar. Had they entire back end not been ripped off then it would of never been checked. Not the point. The point is that just cause there's a little rust on that thick reinforcement bumper bar that is still very well intact and attached to the car, how can it be used against me as a pre existing damage. It has never had rear end damage and it only has 85k miles. They are try to appraise it at 5100.00 then subtract that 1775.00 from this "pre existing damage". How to I handle this to get the full 5100.00. I really need every dime to get a another car