auto accident, please help

Hi Folks,

I was hit by car which is insured by Farmer Insurance. My car
insurance help me to file a claim against Farmer Insurance. It is clearly other party's fault, since he hit me at real bumper.

However, Farmer Insurance send me a letter indicate it can't
reach his client, therefore, Farmer can't take the fault. I know
Farmer doesn't try very hard to talk their client, since they never returm my call, nor answer my call. Now my claim is dead.

Any suggestion or idea please ? Should I sue Farmer Insurance or other party ? Thank you very much for your advice..