Update Paused L4D2 bug?

[CrumbledyCrop]

I've had my L4D2 for a while now and after I came back from a trip I found that in the steam library it was stuck on Left 4 Dead 2 - Update Paused.
When I try to resume updating, nothing happens
When I try to run the game, it says the game is currently unavailable
Restarting Steam does nothing, and forcing steam and left 4 dead 2 to update does nothing either.
Re-installing the game is an unfavourable option because of VERY slow download speed and low internet cap.
What do forums?