I'm not sure whether you booked directly through Costa Cruises or a Travel Agent. If you booked through a Travel Agent, call them to see what they can do about giving you funds to cover costs, etc. This is another good reason to purchase travel insurance right after you book a cruise.
If you do decide to cut loose, so to speak, check the cancellation policy on your cruise contract. I don't remember what the deadline is, but I'm not even sure if you'll get any money back.
Also, I would suggest, as another person mentioned, maybe posting this in the "All other cruise lines" section, as you're referring to Costa Cruises, and not Carnival Cruise Lines. Just send a private message to one of the admins, and they can probably move it.
2007 - Majesty of the Seas
2009 - Enchantment of the Seas
2010 - Freedom of the Seas