Easy to say from the comfort of my terminal, but some urban advice:

Remove the chains and get out; most important is your freedom and safety. They aren't going to risk prison for assault and battery. If they give you trouble, call the police immediately. Take a photo of them and text it to a friend. Don't act intimidated no matter what; it just makes them think they are getting somewhere with you.

Then offer a reasonable fare. If they don't accept, offer to call the police and let law enforcement sort it out. They'll take the fare.