I guess I don't know why you feel your reason for canceling and wanting a full refund is more important than someone else's. You have been given a solution, and if you cancel this cruise and book the other one at the same time, I think the balance of your deposit will be used toward the new deposit. If you cancel and don't book on the same call, the balance of your deposit gets applied to the final payment. I believe the info I posted is correct, but I personally have never had to cancel an Early Saver cruise I have booked.
You are the one who booked Early Saver and for most who use it, it's a great program. I personally wouldn't use Expedia as we had a problem years ago and I ended up having to go to the state's attorney general to get it resolved.
I can understand your being upset, but keep in mind, you are the one who booked at this lower rate for the cruise. It's not Carnival's fault or the fault of Expedia, it's yours.
Too many people book Early Saver without knowing the facts other than the rate initially is usually lower and if the rate goes down after final payment, you can get OBC. That's all they listen to/for and pay no attention to anything else until they run into a problem---then it's never their fault or feel that they should be exempt from the rules because they are who they are.