If you buy a ticket and then choose not to travel, you are entitled to a refund from the original retailer or Train Company who sold you the ticket. Unless the terms and conditions of your ticket (Advance Tickets for instance) indicate that it is non-refundable.
All refund requests must be made within 28 days of the ticket expiry date and if you have a physical ticket this will need to be returned to the retailer of the ticket in order to obtain a refund. A £10.00 administration charge per ticket is applicable unless you chose or are unable travel due to disruption or cancellations to the train service you planned to take then in these circumstance no administration charge will be applied and a full refund will also be provided on Advance Tickets.
How did you buy your ticket?