Third party claim rejected

I was involved in an accident where the other driver didn’t follow the proper rules of the road and failed to stop at a stop street (the driver then hit my car). The driver of the other vehicle was insured with Outsurance. Once the collision occurred, the other party admitted liability at the scene on several occasions, with a witness present. I then submitted a third party claim to Outsurance, who then rejected my third party claim - even though their client did not obey the stop sign and basic rules of the road. The grounds for the rejection was that I acted irresponsibly, however I had the right of way, and followed the rules of the road. The pictures submitted along with the claim also show that the statement provided contradicts the reasoning behind the rejection of my claim. Their legal department refused to answer my questions and were very rude to me. They were also very unhelpful and cut short my call. I am now left without a vehicle to use due to this incompetence.