How do I return something or get a refund ?

You can try here:

http://www.apple.com/emea/support/itunes/contact.html

Important: Mention of third-party websites and products is for informational purposes only and constitutes neither an endorsement nor a recommendation. Apple assumes no responsibility with regard to the selection, performance or use of information or products found at third-party websites. Apple provides this only as a convenience to our users. Apple has not tested the information found on these sites and makes no representations regarding its accuracy or reliability. There are risks inherent in the use of any information or products found on the Internet, and Apple assumes no responsibility in this regard. Please understand that a third-party site is independent from Apple and that Apple has no control over the content on that website. Please contact the vendor for additional information.

Apple's general stance is that all sales are final. They will only assist you where there are billing errors in your account, but for other matters with purchases you need to look to the developer for help.