Retrieving unknown Apple email for unsuccessful Apple Pay transaction on MacBook Air

This is the second time I encounter this problem. I pay via my MacBook Air a subscription fee and the App do not receive the payment, which I got an email from Apple and a Bank confirmation.

During the previous time, the vendor complained Apple use an unknown email and they had no idea what email Apple used.

Now if this is the same scenario again, how do I retrieve the Apple email which Apple uses for the transaction.

Please, I paid for a service and now my subscription will expire because of this issue

[Re-Titled by Moderator]