Transmission Replacement Gone Wrong--shop Closed For Over A Week With My Car Inside

Location: Los Angeles, CA

Initially, I was promised a 1-2 day turnaround. I prepaid most of the cost (transmission cost $2,500, I was asked to pre-pay majority of this cost, I paid $2200). On 9/12, I was told the wrong transmission had been delivered (it had more miles than promised). The correct one would arrive 9/15. It was installed, but by 9/16 I was told my car still wasn't driving correctly and the replacement transmission needed to be reprogrammed. This was scheduled for 9/17. Since that date, the shop has been closed.

I have been without my car since 9/12. On 9/24, I received one text message saying the owner had been in the hospital and that his sons would reopen the shop the next day. That never happened. The shop remains closed, with my car still inside, and I cannot get updates. Their phone goes straight to voicemail, I have called many, many times. I have texted. I have sent requests through yelp. I have went in person three times.

At this point, I don't know the true status of my car or whether the transmission was even the real issue (since it still wasn't driving correctly after replacement). This shop has been in business for over 10 years, but I feel stuck and desperate. There's another transmission shop directly across the street that I could potentially move my car to-if I can even get it back.

I need advice:

Is my next step contacting the police or another authority to recover my vehicle?

Given how far this has gone off track, am I still reasonably expected to pay the full agreed amount? (Transmission cost $2500, labor was supposed to be $750--1 prepaid $2200 towards transmission).

How can I best protect myself moving forward?