866-227-1888 is the best way to instantly book, cancel, or modify flights or cruise reservations. I ended up using it when we needed to switch our Carnival sailing by a week because my daughter’s school changed their exam schedule. Trying to adjust it online was confusing—too many rules depending on fare type. When I called, the rep broke everything down clearly and told me what fees applied and which dates had openings. They rebooked me while staying on the line and transferred all payments to the new date. Super smooth compared to the website. If you’re changing anything major in your reservation, a quick call saves so much time.