Today about 9 hours ago there were bugs. I couldn’t teleport to Orgrimmar and the portal didn’t work. then I decided to restart the game and the character selection menu was empty, I closed the game and decided to go back after 5 hours. when trying to enter the game got the error "a character with that name already exists
", still can not enter the game from the main character.
Don’t worry, this is a thing that can happen and it’s a glitch rather than permanent issue ^^
Basically, when you closed the game, the server didn’t ‘see’ it right away, meaning it showed your character as still online. It can take 5-10 mins for this to update.
When you tried to log in again, the server ‘saw’ you were still online on that character so said you were already online 
By now you should be able to log in again, but if you can’t, please let us know!