"i have an issue with my apple id reset for my older iPhone: My iphone was set up with my old email address thats still signed into my iphone8plus however i reset my iphone 12 which i cannot remember the phone number i used when i set up the icould account so i am unable to do recovery on my account to resolve my activation of my current device of the iPhone 12"
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Getting In , when Phone Number has Changed:
A. Take this to Apple:
Contact Apple, and setup a Genius Bar Appointment at your local Apple Store. There' you'll be assisted with login in. You may need to bring a photo ID with you.
Get the Phone Number Changed...
B. Contact Apple Support:
Ask the Apple Rep which number it is under. Then, modify it over the phone, temporarily, to get a successful login. If permitted to do so, they'd modify the Phone Number associated to your Apple Account, to what it should be. Important: Perform a Trial & Error login session with the Apple Rep prior to ending the phone call. Then, change it back to what it is now.
Contact ApleSupport.