Apple Pay is a payment conduit. Only you, and you alone can initiate an Apple Pay transaction. No one else, not even Apple can just charge you through Apple Pay unless you previously authorize the charge. Apple Pay requires your biometric authorization (Face ID, or Touch ID or passcode).
If you subscribed on website or app using Apple Pay, then you alone are responsible for the management of the subscription. Apple can't do anything about it as it's not directly involved. Apple can't explain a charge using Apple Pay because other than managing the mechanism, it has no direct involvement with the merchant charging or with your card issuer.
I know it's frustrating to get charges you cannot stop, but just blaming Apple because you don't undlrsdtandf how it works is not going to help get it resolved.
Go to the website or App that is charging you and cancel it there by logging in with your account there and finding the subscription in the website settings.
If the charge appears as "apple.com/bill". then it has nothing to do with Apple Pay whatsoever and you should be able to cancel it from your Apple Account Settings.
click here ➜ If you want to cancel a subscription from Apple - Apple Support