I think that this is really hard luck but I am not sure that you will get anywhere with a protest. It is almost certainly covered somewhere in the small print of the booking, “circumstances beyond our control” and the like. You obviously booked the maiden voyage mainly because of the kudos of being on the first cruise of this enormous ship and I appreciate that. The only thing I will say that might help is that having been on a maiden voyage I would never do it again because of all the things that can and do go wrong, even after all the trials of “Shake-down Cruises”, and the second cruise is invariably better and smoother……Don’t know it this will help….Nei.
The info your T/A has told you is incorrect...... Royal Caribbean International said passengers already booked on the ship’s original 17 May maiden voyage would be offered first refusal to switch to the new inaugural sailing, which operates the same itinerary (Southampton-Cork-Southampton).