The cancellation policies of shipping companies vary. Cancellation without incurring charges is usually only possible if this is specifically provided in the terms and conditions of the booking. If you want to cancel a booking, you should contact the shipping company as soon as possible. Shipping companies do not usually refund tickets if a booking is cancelled very close to the time of departure.
A refund is usually given if your reason for cancelling is a sudden illness or other unexpected and serious circumstances. You should always inform the shipping company of any such circumstances as soon as possible.