Pepsi's Gift Promotion Letdown

I bought two 2.5-liter bottles of Pepsi Cola with black caps and used the codes on the caps to get two 1-liter bottles of Pepsi Cola for free. But, to my disappointment, the store where I bought them says they don't agree with the promotion and won't honor it. If that's true, why are they sold in places where there's supposed to be a deal? I went to two different places in Ordu that were part of the promotion, and both of them said they couldn't give me the gifts. I don't understand why I can't get my hard-earned rewards. Don't advertise products with promotions that can't be kept if you can't keep them.