Unauthorized purchase - refuse to credit

I am shocked at groupon's horrible customer service. We were traveling for the holidays. I was looking at groupons and put my phone in my purse. Several hours later when i looked at my email, i saw a purchase confirmation from groupon for a $40 final sale food item. I did not make this purchase. When i emailed and later called groupon, they insisted that since the 2 hour cancellation window had passed and the sale was final, they could not do anything about it. I could not believe this response. They said sometimes orders happen accidentially when using a mobile device! I am livid, will dispute this purchase with my credit card company, and will NEVER use groupon again!