If I were you, I would send off for a certified copy of your birth certificate. If you ask real nice, they will send you a copy within a day or two.
That way, if you don't have your passport back (and your original birth certificate) you will have a certified birth certificate from the agency that issued it, and that will be enough.
I lost my birth certificate many, many years ago, and before I got my passport I had to get a certified copy.
Look on the bright side, you'll have that passport for your next cruise! Good luck and let us know what happens.
Carnival Elation March 11
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Carnival Glory Sept 04
Carnival Fantasy Jan 04