Many online retailers, including play.com may be breaking the law when they either don't accept goods that have been opened or not refunding the delivery charges.
Check these links:
http://webarchive.nationalarchives.gov.uk/+/http://www.berr.gov.uk/whatwedo/consumers/fact-sheets/page38102.html#Q3IunderstandIcanchangemymindifIdonotwantthegoodsorservicesDoesthatapplyinallcases
http://www.bbc.co.uk/blogs/theoneshow/consumer/2009/08/27/get_your_refund_distance_selli.html
http://news.bbc.co.uk/1/hi/business/10560466.stm
http://www.bbc.co.uk/northernireland/oyb/goods_services/distance_selling_regulations.shtml
Check these links:
http://webarchive.nationalarchives.gov.uk/+/http://www.berr.gov.uk/whatwedo/consumers/fact-sheets/page38102.html#Q3IunderstandIcanchangemymindifIdonotwantthegoodsorservicesDoesthatapplyinallcases
http://www.bbc.co.uk/blogs/theoneshow/consumer/2009/08/27/get_your_refund_distance_selli.html
http://news.bbc.co.uk/1/hi/business/10560466.stm
http://www.bbc.co.uk/northernireland/oyb/goods_services/distance_selling_regulations.shtml