I agree with Mike. Let them know you are not happy and you want more than just a refund. Be specific in what you feel is fair compensation. A future cruise credit, OBC on a future sailing...etc.
Many people need to allocate vacation time and other schedule changes in order to book the cruises. Although it is completely within the cruise lines rights to cancel the cruise and accept a charter it still can cause financial and logistical hardships to those whose cruises are canceled.
Take care and I hope you find a wonderful replacement cruise.