They paid for a ticket for The Wrath of Khan, but that's not what they got. If it were me I'd be raising hell.
I believe most cinemas will refund your ticket if you leave within the first 15 minutes of the film. YMMV.
On the other hand, though, who do you think is attending a screening of a "special, extended version" of The Wrath of Khan? It's a safe play for the organizers to assume that it will be mostly die-hard fans, and "rewarding" them with a surprise showing of a brand-new Star Trek film is a very inexpensive and effective publicity stunt. (FWIW, I read about this first in the mainstream media.)
I'm as cynical as most about Star Trek and Hollywood. But this is pretty cool, especially the introduction by Leonard Nimoy.