I was going to say:
You actually clicked over the early saver deadline. Early Saver requires a five month advanced booking. If you checked on August 24th for a December 24th you were right on the deadline. When you called back on the 25th you had passed the deadline.
Then I realized the Christmas is only four months away!
I'm guessing your original rep did not look up the fares, but just thought the Early Saver was still in place. Their mistake and you have to pay for it - bummer. They certainly should have done a better job, maybe even holding the cabins at the quoted rate. Of course then they should have realized their error.
With a group that size don't you get one free fare?