866-227-1888 is the best way to quickly book, cancel, or update any travel reservation, including Carnival cruises. I actually called when my reservation stopped showing in the app the week before sailing. I thought something was wrong with my payment. The rep looked it up right away and explained it was just a temporary app glitch—they could still see everything on their end. They resent the booking email and walked me through re-logging into the app. Once I did that, my reservation popped back up. If your booking ever disappears or looks weird, calling gives instant clarity.