Who did you book with - T/A or Celebrity direct? Who ever it is call them and speak to them, but if you have cancelled you will have lost your deposit which is a shame as they would/could/should have swapped you onto an alternative cruise. It does clearly state in the T&Cs that flight routes are not direct and not guaranteed. The Glasgow flight may be with a carrier that X do not have a contract with, or may be sold out of their allocation - you should have asked.
As A of N says it is always worth talking to someone before you take drastic action. If you are still able to keep that particular cruise booking you may be able with some astute negotiation to turn it into a "Cruise Only" booking and make your own bookings for flights. transfers and hotel overnight stay, (make sure you do the overnight in an hotel in case of delays) They don't want to lose you ( unless you said something rude to them when you cancelled). .... Neil.