diamond car insurance

I was hit from behind by a driver doing a u-turn in the street at traffic lights. i came through the traffic lights, and as i passed, he proceeded to continue with the u turn and rear ended me, denting me badly. There were no witnesses. Diamond Car Insurance refused to support any claim by me on his insurance, despite me being hit from behind. eventually after months of wrangling, they said they would settle 50:50! I declined and got a better insurer