Discovery insurance is robbing us really.

My car was damaged in an accident that was caused by their client, but now they are only paying 60% of the damage costs, and they are saying they don't pay for fully damages because I could have avoided the attached, that is their reason, I don't understand why are they saying that because I was driving my car and there was no way anyone could have avoided that, and the problem that they only assume that I could have avoided it, what also surprises me is that their client was insured for fully comprehensive, meaning they must pay for all the costs, that shows that claim pays for all the damages but they are paying satain potion of the costs and keep the other potion for themselves, that is a day light ******* for the poor people, I wrote to hello Peter last week Wednesday for this problem, they got the message and promised to review the offer and they will come back to within 24 hours, they didn't and I phoned them again today and they said they are still on their original offer. So is there anywhere I can get a fair treatment regarding this? Please help. Thank you .