In-app payments are handled through the App Store, Google Play, Amazon Appstore and Chrome Web Store. Visit the following links for assistance.
For Apple support, visit https://expresslane.apple.com and select your device, then App Store.
For Google Play/Android Market support, visit http://support.google.com/googleplay/
For Amazon Appstore, visit http://www.amazon.com/gp/help/customer/display.html?nodeId=200551840
For Chrome Web Store support, visit https://www.google.com/support/chrome_webstore
To request a refund, please review the following article