As is the case with most in-app or software purchases, purchases in the game are non-refundable. There can be some exceptions in special circumstances however. Since the process is controlled by Apple, Google or Amazon you would need to reach out to their support teams in such circumstances.

Android:
https://support.google.com/googleplay/#topic=3364260

Apple:
https://support.apple.com/en-gb/HT204084