I don't know if I understand correctly.
You paid $650 to attend some parade. After the excursion you found out that another cruise line charges less. So you are upset now that you paid more for an excursion on one cruise line then you would have on another.
a) sorry to hear that
b) unless I am being flown by private helicopter I would never pay $650 per person for any excursion
c) does Carnival offer the exact same excursion?
d) you won't get far with any customer service since you were obviously willing to accept the price in the first place
Little advice from me: It always pays off to do research before you travel rather than afterward.