I see the Welcome back screen with someone else's name when creating a new LINE account
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When creating a new LINE account, someone else's name may appear when you verify your phone number. This happens because the LINE account of a previous owner of the phone number is being displayed.
If you see a message that says, "Welcome back, XXXX!" and don't recognize the account, tap No, that's not me and proceed with creating a new account from No, create a new account. Once you finish creating your new LINE account, the phone number registration will be removed from the previous owner's LINE account.
See also:
Registering/checking/changing your email address and password
Creating a new LINE account
Transferring your LINE account with a different phone number
Changing to/registering a phone number from a different country