So I call to cancel. They say "don't bother cancelling". Just ignore the fact that I'm not going to fly. In a few months, long after I didn't show up for the flight, just call in with the same confirmation number, and voila! all will work!
Not true... if you no-show, they cancel the full ticket without anything coming to you. Cancel the flight & have them give you a credit. Call back and immediately re-book your new flights. If they won't cancel, do the usual "hang up & try again" or ask for a supervisor.