Bad claims handling

Ive been sitting with this query for a while and keep on getting the same response. I am a third party to a person that is insured with Cib. There compost driver drove into me and now I am liable for a portion of my own damages. Cib is asking the client who was not even present at the accident whos fault it was and they are going on what the client said and not the driver of the truck. This is absolute madness. How can they determine the pay out of a claim with people that was not even their????