If the event you have purchased tickets for is cancelled or postponed, you should notify the seller in order to receive either a refund of the amount you paid for the tickets excluding the buyer's fee, or replacement tickets for the new event date, depending on the particular instructions issued by the event organisers. 

If a refund is provided by the seller, it is not required to include a refund of any delivery costs, and you will not be entitled to claim any associated costs such as travel, accommodation or loss of earnings etc.