Something is not right here. As already posted the Cellar at Sea does not go on until 12 miles out of US ports. I always leave my cell on until we are down to a bar sailing away. Also I think Cellular at sea show up different than International charges but I could be wrong.
You have not said who charged you. If it is ATT you need to asked for a complete bill showing times and dates of charges. If you were charged while in US ports you need to dispute it.
finally if you have ATT I suggest signing up for the ATT International Plan. It is automatic so no major mistakes in foreign ports. You get charged $10 a day for unlimited data, text and calls. You are only charged if you use it. This does not cover Cellular at Sea when the ship is between ports.