Hello,
I play eso since april 2017, my gt is croma lopo and when I try to lunch game they ask me to enter my user I'd and password but my account isn't bound to any eso account. And I can't bound my xbox account to my eso account.
Linking an ESO account to an Xbox Live Gold account or PSN Online ID is done through the console's interface. Once the game is installed, you will be prompted to either log in or create an account. At that time, you will link your ESO account to your console version. You can link only one PlayStation and/or Xbox account to a single ESO account.
If you continue to have issues you can open a ticket with customer support.