I think I've paid twice for the in-app purchase!

iOS / iTunes

The Premium upgrade is a subscription and can't be purchased twice with the same Apple ID.

Apple unfortunately does not allow us to refund you directly. If in any case you think you've purchased it twice, please sign in at Apple using your Apple ID:

https://reportaproblem.apple.com/

There you can see a list of your in-app purchases. If you see in the list that you've paid twice, you can report it to Apple by pressing the button in the list.

Google Play

The Premium upgrade is a subscription and can't be purchased twice with the same Google account. 

If in any case you think you've purchased it twice, please contact us and send us your order numbers or transaction IDs.