Shared office is messy to the point that I can't do any work, how to proceed?
To add another perspective: You write that everyone else is doing fine, and in fact is doing productive work. I know that people have very different working styles (in our department, all office space is 'flex-space', i.e., no-one (including full professors) has an 'own' office and people have very different preferences whether they want to sit in a more quiet place or a more social stting), and it can very well be the case that you are not productive in a setting where others are.

Nevertheless, I think you should consider the possibility that it is actually you who has the problem, not the setting that is the problem. If there is no easy solution (i.e., a different space for you), then, in fact, I guess it would be unreasonable to expect 11 people to adapt their working style rather than you (1 person). 

I do not mean this negative at all, but there are solutions to work in a busy place, like putting on headphones and the like. Have you considered such options?

Good luck!