Before we could even begin to help you we need to know more - when does the cruise sail? have you made full payment yet?
If it is more than 90 or 100 days out you may be able to get a full refund.
Between 90 and 30 days you get a partial refund and after 30 days there is no refund.
BUt they should have told you all of this when you called to try to move the cruise.
It is too bad you did not use a travel agent. They would have told you the chances you were taking by not having insurance - and they would have tried to process a refund for you immediately the day you knew you needed it.
Also - sometimes (not a certainty) the better cruise agents have at least some clout. She my have gotten you at least a partial credit for a future cruise.