settlement question

My wifewas rear ended in Sept, but a hosptil mini bus, he was cited for failure to control vehicle and following to close. They paid to fix our car and asked for medical records an verify employment. My wife missed 2 days of work, has been seen by the doctor 2 time and now if going to phisical therapy. The insurance called 3 days after the accident and offered 500.00 we said no. That is all we have heard, we called and told them she was going to therapy and heard nothing. The issue is we are military and don't pay health care, so I have no medical bills. we were thinking of doing a demanding letter, but not sure for how much. Any help on our next step?