Next cruise certificate

I bought a next cruise certificate December 2015, I have had to reschedule the cruise I was going to do this November using it. My TA is telling me they now want to charge me a $100 date/ship change fee. I know this is a new policy but can it apply to a credit I bought 2 years ago? Not making me very happy at the moment.

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Unless you changed your booking to a non refundable rate after July of this year then the information that your TA gave you is incorrect.