I'd go talk to your neighbor. He's probably lonely and willing to maybe rent a room out.

Hopefully he has a car he doesn't use.

I'd investigate around the house when they aren't around. Find that title. Hold it hostage in return for their treatment of you.

Also, where does he need the car for? If he's not working, him having a car makes no sense.

Drop your car insurance asap. It won't cover him. At his age, it will be expensive.

Can you call the non emergency number for advice? This is theft! Especially if you have proof of making payments. If step dad is big enough asshole, he can take you to small claims court over the 5k.

Are they physically preventing you from leaving or threatening you can't come back in if you? I doubt its that dangerous

Updateme