Are you still over the Pacific? If so, how do you know you were bumped? Was your first flight delayed such that you would misconnect? Did your original second flight cancel?

Basically, if you're holding a confirmed reservation, you are entitled to fly on that plane. I'm still rather confused as to what happened. But a polite but firm exchange with a gate agents (and possibly a supervisor) might be needed to correct this upon landing. I don't know how tight your connections are, so you either should go to the gate directly (if you flight will be boarding in say T-45) or to a CS desk or call