Auto Accident

I am in IN. I was rear-ended while parked at the side of the road. My car is a total loss. The insurance for the person who hit me contacted me to say they would only accept 75% of the fault because I did not have my hazard lights on. In the time it took me to pull over, put on my emergency brake, and look up in my rearview mirror, I was hit. How do I get the insurance company that accepts most of the blame to take all of it?? Do I have to take them to court? Currently, I am incurring expenses because this is not resolved, and I have to rent a car. I would appreciate advice for dealing with the hitter's insurance company. My insurance company will not assist. I am wondering if I get a lawyer will I end up with the same amount or less in settlement due to legal expenses.