All purchases in the game are processed by the store from which you downloaded the game. To obtain a refund, you need to contact the support service of your app store.

To speed up the refund process, we recommend that you provide detailed information about your purchase: the order number, the time of purchase, and/or the payment receipt.

To cancel a purchase in the App Store: https://reportaproblem.apple.com/?s=6 
To cancel a purchase on Google Play: https://support.google.com/googleplay/contact/play_request_refund_apps