I detest the concept that we need yet another "law" before we can actual enforce anything. There are plenty of laws being broken already, we should go and prosecute them before we start making up new ones to ignore.

I had something similar happen in Germany, on the way from the (international) airport to a hotel the driver started some kind of spiel that suddenly his banking machine had broken and he couldn't take card payments. My friend/colleague Jaap who was with me said we'd pay cash and I said no way, and after fiddling for a bit with his phone (mine wasn't a smartphone) gave the driver a different address. When we ended up in front of the police station the driver became a lot more friendly, drove us to the hotel instead and suddenly found that his banking machine had miraculously started working again...

I find that by giving in to such fraud I'm helping to perpetrate it so I've vowed not to let it happen, at the same time there is always a chance that such an interaction would turn violent. After all, they've already decided they want to steal from you. My weighing of this is that they have more to lose than me because I'm a transient and they are not.

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.