Can't see people in orgrimmar?

Q u o t e:
I have [Veteran of the Wrathgate] Achievement though. So I did the entire quest line.

The achievement is actually awarded in the middle of the quest chain, not at its completion. You survived the treachery at the Wrath Gate, and that's something to mark in the annals of your character's history ,but there's still work to be done. :)

Now, on your Tauren specifically, it appears you have not yet completed the Horde-version of "Return to Angrathar." This quest is offered by Alexstrasza. You should find her at the top of Wrymrest temple, looking scorch-y in her human form.

If you don't see this quest offered, let me know, and I'll be happy to troubleshoot with you further.

Mind logging out really quickly for me? I'll take a peek. :)

Ho'kay, so. "Return to Angrathar" is now complete, so you should be able to proceed with this quest line by speaking with dragon-form Alexstrasza in the main courtyard of the Wrath Gate. :)

If you continue to experience any further issues, Untoldstory, please let me know.

Your character was simply stuck in the wrong phase. It happens. :)

Q u o t e:
I finished the battle for undercity, shouldn't Orgrimmar be back to normal?

Hm. That's no bueno. =/

I'm going to have this issue investigated further for you, Untoldstory, but it may take some time. We'll get this figured out as soon as possible, though. Thank you so much for your patience!