Geico Insurance Geico, Geico Refuses to Cover Entire Claim San Diego California

We were rear ended in a mall parking lot by a teenage driver. Our vehicle is a 2006 Acura TSX. We were stopped waiting for the car in front of us to turn down a parking lot isle when the driver rear ended us at approximately 10-to-15MPH. Immediately after the incident a clunking noise began to occur when we braked and turned. Geico clunking noise began getting worse. Geico referred us to Mossy Toyota Body Shop in San Diego for repairs. They covered the replacement costs of a new bumper and determined the clunking noise were the front strutts. They clamied the strutt damage was not caused by this accident rather it was just coincidental. I called BS and confronted them. They re-evaluated the car and called back now claiming the clunking is not the strutts rather the steering linkage. Again, they claim the damaged linkage was from normal wear-and-tear and not from the accident. I find it funny the car began clunking right after being rear ended yet Geico claims the damage is not from the accident  and refuse to fix it. Not sure what we can do now -- does anyone have any recommendations please? Is it possible to sue Geico?