Well if it was me in this situation I would go straight to the restaurant and talk to management. It sucks you have to do this, but I know from experience that people talk a different story in person than on phone.
Check the Groupon website for corporate contact information. Avoid customer service at this point.
Look for HQ or try find another number to call or maybe visit the restaurant or call the restaurant. Somebody got to tell you something. Companies don't like talking to humans so you may have to do some emailing
Thanks! Your answer is awaiting moderation.