Received message that my apple i d and phone number are being used iMessage on a new iphone
What to do
iPhone 8, iOS 15
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Check your device list to see if there is a device signed in that you don't recognize. You can remove the device using the steps in the article below. As a precaution, change your password.
Apple ID device list -Check to see where you‘re signed in. *
See who has access to your device or accounts
ASC YouTube for How to reset your Apple ID password
What to do after you change your Apple ID or password - Apple Support - I suggest doing this before you change your Apple ID or password.