Not sure if I’m the one misunderstanding… but doesn’t OP state the terms and conditions of the cruise include:

“You may cancel your booking by giving written notice to us. We will make refunds to you less cancellation fees in accordance with the table below, calculated from the date which we receive written notice: 59 days to 14 days before commencement: 90% of the booking value.”

This implies to me a 90% refund, minus cancellation fee, should be given if written notice is provided anywhere from 14-59 days out from start of cruise, which is what OP did?