All payments are processed through the Apple or Google Play stores (depending on your device). If you would like a refund for an in-app purchase, you would need to contact the respective app store.
 

For iOS (Apple) devices

All purchases made from an Apple device are managed and processed through Apple. 
If you would like to make a refund for a purchase you will need to contact Apple to request a refund, please follow the steps listed on their support page: Request a refund for apps or content that you bought from Apple
 

For Android (Google Play) devices

All purchases made on an Android device are done through the Google Play store. If you would like to request a refund for a purchase please follow the steps listed on their support page: