I understand what you are saying about involving the credit card company, but shouldn't the charge be showing as from the cruise line, not the TA? I know when we do a charge through our TA, it shows on our statement as being a charge by the cruise line. And there have been posts warning others that the charge should always show that way, not as a charge to a travel agency.
I would think they would do the charge back to the cruise line, not the TA.