Not to be one-sided, but Carnival said "non-refundable" travel costs. If you can still use a ticket do you really expect Carnival to pay you for it as well?
Do you promise the send the money back to Carnival if you end up using the ticket to go somewhere else in the next year?
I am the editor, but I also speculate, ask questions and play devil's advocate. I reserve the right to change my mind.