Unfair settlement

I had an accident with a Zurich client on 13 March 2015 and they told me that their insurance would pay for my car's damages. I have been patient with them for five months and yesterday they send me an offer. they are offering to pay 70% of the costs and on top of that they are subtracting 30% of their client's damages. They said they are also holding me responsible for the accident that I should have avoided the accident. How do I do that when their client just went in without checking if it was safe for him, and mind you, there is a stop sign on the road that the accident took place. My problem is that they didn't tell me about this 70/30 apportionment all along, this only comes up when they have to pay. I refuse to be ********** like this, I think I will let a magistrate decide on this one