Contact Apple here:
Contact Apple Support - Apple Support
Not sure how Apple Pay was used to make a purchase you did not agree to . When using Apple Pay, you have to authorize the charge with the amount showing on the screen, followed by verification with FaceID/Passcode. It is not something that can be done by accident.
Also, not sure if this was an in-app purchase, since in-app purchases do not use Apple Pay and bills the payment method you have on file for your account. In most cases purchases in the App Store are final. At times, Apple may offer a compassionate refund, but it should never be expected.
Request a refund for apps or content that you bought from Apple - Apple Support