Hi @kimannhan!
Nothing much more frustrating than not being able to login to your AT&T account. I’ll be happy to help you!
It seems like your browser may not behaving like it should. Have you tried clearing the browser cache?
I would recommend trying that first and if it does not fix it, try using another type of browser, or head on over to our mobile site at https://m.att.com/myatt/#/login where you can also manage your account including adding an international plan from your PC’s browser.
You can also download the myAT&T app directly to your smart phone. It provides account management for all your AT&T services. You can get it by going to att.com/myattapp from your phones browser or from your device’s app store.
Please let me know if this helps and have a great day!
Demetria, AT&T Community Specialist