My rear driver side little window on my Chevy Silverado window fell off on the freeway

Question Details:

I was driving n bound fast lane next to carpool lane on 110 fwy. window flew and hit the lower end of the the divider.  I looked and saw a car pass after a few seconds. Person went around me and sped off. I flagged the driver but the driver sped off. My friends were behind me and saw the window hit the divider not the car. I recieved a letter that I owe $6500. I didnt see the damages or speak with the driver. I was going to let the judge decide on this matter.  I dont know if there is anything else I can do. Please advise Important Notice