If the purchase was made on an Apple (iOS) device: All refunds are handled by Apple, who you can contact at http://www.apple.com/support/itunes/contact/

Please contact us directly through in-game support by going to Settings > Help & Support and tap “Contact Us” in the upper right hand corner. In your message please add the receipt of the purchase. The transaction ID (looks similar to this - GPA.1234-1234-1234-12345) at the bottom of the document must be visible. Receipts for transactions have been emailed to you by Google after each purchase.