Delete old telephone number
My iTunes has an old mobile number which is not in use so I cannot sign in. I cannot remove the number & cannot find it at all under my settings on my iphone
Go to Settings > [your name] > Name, Phone Numbers, Email. Next to Reachable At, tap Edit. Tap Delete next to your phone number and follow the instructions. After you enter the mobile phone number that you want to use as your Apple ID, a verification code is sent to you at that number.