How can I cancel a fraudulent Apple Pay transaction?

Only the merchant can cancel a transaction. Please contact the merchant. If you believe your credit or debit card is compromised, contact the fraud department at the issuing bank. The number is printed on the back of the physical card.

Was there a payment verified in your billing data, or maybe this was this a mail message or text message claiming it?

Because phishing scams claiming questionable payments held or fraudulent payments made are common.

If this payment was actually made, then it’s between you, the vendor, and (if you didn’t make the payment) your payment provider (as mentioned above) for cases involving fraud.