My question involves an injury that occurred in the state of: PA

A tractor trailer ran a stop sign last week and hit me on my driver side. No injuries. It was at a 4 way stop, I was just pulling out and he hit me going about 35mph. The truck was in violation of a weight limit for the street he was on and (obviously) ran a stop sign. My car, an '01 civic was totaled. My insurance company contacted me and offered me the cash value of my car. I'm not satisfied with that offer and was just wondering what my options are? I have not spoken with the other agency. Is it my insurance company's duty to act as a negotiator between myself and the other agency? Or is this something that should be handled via a 3rd party? I'm just trying to understand what my rights are. I'm not looking to retire here, but I won't be able to replace my car with the amount of money offered. Bottom line is my car was payed off and would have last me another 5 years and now it's toast. I appologize if this comes off as a rant I'm just a bit upset. If there are any more facts I can provide please let me know.

Thank you ahead of time for any help.
Dave