Offers like that are typically subject to availability, and they always have a disclaimer somewhere on their website. So there is nothing you can do about it.
I couldn't find the page with the rate you posted about, but here's their disclaimer for their European deal:
"*Rates are USD, per person, double occupancy, cruise-only valid for new retail bookings for U.S. and Canadian residents. Rate shown is for a Guarantee on the Nov. 20, 27, Dec 4, 11, 2016 and Jan 1, 8, 15, 22, 2017 sailings aboard MSC Splendida. Government fees and taxes (GFT) for all sailing guests are additional. Passengers booking inside stateroom (category I1, I2) - receive $50 per person (max $100 per stateroom) SBC. Passengers booking ocean view stateroom ( category O1, O2) - receive $50 per person (max $100 per stateroom) SBC + $50 per person (max $100 or 20 drink vouchers per stateroom) beverage package; Passengers booking balcony stateroom (B1, B2) - receive $200 per person (max $400 per stateroom) SBC + $50 per person (max $100 or 20 drink vouchers per stateroom) beverage package + dinner in a specialty restaurant for a maximum of 2 persons; Passengers booking Aurea balcony (B3) or suite (S3) - receive $250 per person (max $500 per stateroom) SBC + dinner in a specialty restaurant for a maximum of 2 persons; Passengers booking Yacht Club receive $300 per person (max $600 per stateroom) SBC. Specialty dining package is not available on Lirica class ships. MSC Club discount is applicable. A discount of up to 10% (not combinable with MSC Club discount) is also applicable to active and retired U.S. and Canadian military, civil service and interline personnel and their spouses, dependent children, parents, and parents-in-law. Qualifying guests must present an I.D. badge from their respective organization at time of booking. Offer is capacity-controlled, subject to availability, cannot be combined with any other discount or promotion and may be withdrawn without notice. MSC Cruises reserves the right to pass on any fuel surcharge without prior notice to all guests. MSC Cruises reserves the right to refuse to honor any prices/sailings that are erroneously printed or quoted. Other restrictions may apply. Ask for "All In " when booking. Offer Expires December 31, 2015. Ship's registry: Panama."
They put it in small print at the bottom of the website.