It is very simple, usually when you cancel a MSC cruise minimum 20 percent of the price is the cancellation fee. So MSC certainly will never give you the current price if you want to upgrade or change after a price drop.
For whatever reason, maybe legal stuff, MSC US customers can cancel for free if they do it long enough before the cruise. That confuses MSCs famous IT, so don´t blame the agent. There is no solution to this.