Contact iTunes support and ask for a refund at https://www.apple.com/emea/support/itunes/contact.html
You realise of course, that Apple cannot recover this from your system. On the receipt is a request to 'report a problem'. Report this as your problem but be aware it is probably a one time situation. The next time they could likely refuse.
You can go to http://reportaproblem.apple.com
You can report an issue with the App, and request a refund, but remember that as per the terms and conditions of the iTunes and App Stores all sales are considered final, and Apple is under no obligation to refund you the money.
App Refund
