@DebInAntigua That doesn't sound right at all. When you changed to the new ship/sail date I'm pretty sure you should have been charged the Taxes/Fees/Port Charges for the new sailing at the time. I confirmed this on 2 reservations I currently have booked that I moved from different sailings.
Edit: And yes I suspect when you get on the ship they will know nothing about it!
On the other hand when I reprice an existing sailing the taxes/fees are never changed and remain the same as when I did the original booking, only the cruise fare/promo is adjusted.