Cruise Vacation Center will not honor their coupons YONKERS, New York

I purchased four vouchers each for $399 discount from Cruise Vacation Center in August of 2011.
Voucher states "Limit one voucher PER PERSON PER STAY".Cruise Vacation Center told me when I booked that a mistake was made but they would honor the already purchased vouchers. In September 2011 I booked my 2011 cruise and received the $798 credit for two of my vouchers. 

When I went to book the 2012 cruise and use the remaining two vouchers, I was told I could not use both
and they would not honor them (even though they state "Limit one voucher PER PERSON PER STAY" ).
In August 2011, Christine spoke with a manager there and she  guaranteed me that Cruise Vacation Center would honor the already purchased vouchers and that I could use them this year for my 2012 cruise.  Of course, she no longer works there.