@luk1337 I assume they use another iDevice to log in and access iCloud from there. The scammer asked to see the utility bill to make sure you were getting green power.
(I heard the start of it, but when I realized he hooked, I went outside. Couldn't stop the actual scam, but I at least managed to give warning).
EDIT: I think FaceID is per device (I don't use ipersonally), but I think more so you can just access to a utility bill.