Don't give up!
There are cancellations all the time. Especially really close to the actual cruise date. Keep calling and ask for each one of your vacation days. You may get lucky.
I was able to get the Illuminations cruise one trip 3 days before we left. It was for the first night we were there. What a great way to start the vacation. I was even able to surprise my wife since it was so close to time to go.
Keep trying!