Welcome to NY. You got ripped off. Sorry.
This isn't a CO/UA issue. They gave you a (in my opinion good) alternative, which you accepted.
If you ever have this experience again (and I hope you don't) take a picture of the cab's medallion ID using your phone. When you arrive at your destination summon a police officer. The cab driver will gladly accept the voucher, and nothing more, at that point.
The driver could lose their medallion (license to drive a cab) if they are caught doing something like this. And those medallions are not, at all, inexpensive.