Why is Apple charging me double the amount for Royal Kingdom?

Re: I bought coin packages on Royal Kingdom app. Then Apple Pay charged me double.

How do I get a refund on the over charge?

For Apple Pay:You can: Track orders and purchases in Apple Wallet - Apple Support

Eg: If it is a subscription you might be charged for April, and then for May so payments are for the month ahead

View your purchase history for the App Store and other Apple media services - Apple Support

See how to: Get a refund for purchases made with credit or debit cards using Apple Pay - Apple Support

or

If appropriate: how to: Request a refund for apps or content that you bought from Apple - Apple Support

More info, if needed:

About purchases not billed through the App Store or the App Store’s In-App Purchase system - Apple Support