Yes, there was an open cancellation period, but OP didn't cancel during that period. It was approx. 2 weeks back in Nov. right after the policy change was announced.
Yes,
DCL allows you to cancel within 14 days of embarkation without penalty. BUT the OP didn't wait until that 14-day window to move her cruise, she did so within the 15-59 days of embarkation. That is a nasty little window that carries penalty forward -- no immediate penalty moving the funds to a new date, but the penalty carries forward and will take effect if OP decides to cancel the future cruise.