Ask your US Senator or Congressman for help. That's kinda the only option, they can try to push on your behalf and USCIS has to respond to their requests. I've done that before while cutting it close on expiration and got an answer that was basically "it'll be done when it's done" and then was approved the next day since I guess that someone had to take my case out of the stack to see what's up and then just approved it since it's already out.