Auto Insurance Debt Collection?

I live in the state of California.

I was in a car accident about a month and half ago in my roommates car. Unbeknownst to me, the insurance on the car had lapsed. I also do not have my own insurance (do not own a car). The police that showed up on the scene was a "Police Services Officers" not a sworn patrol officer, and made many errors and ommissions on the report, and found me at fault. The PSO's are only supposed to respond on non-injury, "minor" property damage calls. I was injured, and the guy that hit me drove through the front of the car w/o stopping and totalled it - I don't consider this "minor". I am currently in the process of contesting this report and filing an official complaint with the police department.

That being said, about 5-6 days ago I received a letter from a collection agency on behalf of the other driver's insurance, saying that I owe $5.500. Nothing was itemized, and I did not receive any debt validation of any kind from them so far. The letter they sent says less about the supposed debt, and instead just goes on and on about how they could have my license taken away if I don't pay "IMMEDIATELY".

As of now, there has been no judgement made against me, and while the PSO stated in his report that I was at fault they did not issue a traffic citation or ticket of any kind.

I have read that you can wite a debt validation request to the collections company and they must send proof I legally owe the debt. After that though I do not know what happens, would they take me to court? At this point I'd prefer going to court so I can show how the botched police report inncorrectly assigned fault to me. I went to legal aid here to get advice, but they can't see me until May 19, and I know I only have 30 days to write the DV request, so any advice is greatly appreciated.