Constant Disconnection problem

I returned to this server yesterday and when I tried to enter with my account ingame (I want to play on Neltharion) everything was ok but just 5 seconds after logging in with my account (5 second on the characters screen) I got disconnect (This thing happens on both Cata realms). I tried everything (deleting cache, reinstalling the client, checking firewall, restarting internet) and it is always the same - login => 5 seconds => disconnect. My friend tried with his account and the same thing happened (also got dc'ed after 5 sec). Where is the problem and how can I fix it?

https://www.youtube.com/watch?v=s88r_q7oufE kek