Have the same issue starting this morning. I enter the login screen, enter credentials, then receive message "Disconnected from the server" instead of realmlist or character select screen.
Tried deleting WTF-Interface-WDB folder, didn't help. Tried removing config.wtf. Didn't help. Tried reinstalling the client, didn't help.
One thing people advise on RU part of the forum (someone have similar issues today) is check by direct network connection if you use router - insert the cable right to your PC network socket. I can't check it due to cable length limitations. Going to try VPN as I suspect that can be network provider related issue, either on my provider or on some new Nost anti-DDOS settings.
If you can try direct connection or VPN, please try and let me know if it helped.