Family Dollar complaint: Ad price was not honored

On August 4th I went through the weekly ad which began on August 4 and I saw that Dr. Pepper was on sale 3 for $12 and if you can track my sales through my phone number you will see I buy Dr pepper almost every visit but I had just gone through a procedure for my health and I wanted to take advantage of this special so I went and as usual bought more than what I needed. While paying I was in shock because I thought it was too much for my calculations but because the line was so big I figured i was imagining it. I looked at the receipt the next day and I saw that I was charged 8.50 per pack so instead of $12 I paid 25.50 plus tax and bottles. I told the manager about the situation and she said to bring the Dr pepper back but I had already opened it and legally Family dollar was false advertising because I winded buying more than what I went to buy.