Dollar General Would not honor shelf price Pearl River New York

I went to purchase an AT&T GoPhone and card today. I seen the price earlier last week and asked the girl how the phone worked and If the price maked which was $10.00 was correct and she sait It was. Today Jan. 2, 2016 I went to purchase the phone & a $10.00 prepaid card. At the checkout the phone rang up at $15.00 NOT $10.00. When I stated the price marked was $10.00 she told me she could not override the price. I would have to pay $15.00. I was going away for the weekend and could not argue, so i took the phone. I think I sould have gotten the phone for the $10.00 shelf price. The store ripped me off for 5 bucks