An Innocent Can of Coca-Cola

I went to the Giant supermarket in Pusat Bandar Damansara today. I bought a can of Coke (the drink, OK?). It was adorned in nice red and yellow colours. It said: "Celebrate the Festive Season with Coca-Cola". The price on the shelf in the cooler said RM1.19. I went to the cashier with RM1.20. She gave me back 11 sen. I looked at the receipt. It cost RM1.09. I believe this was a funny way of looking at contract law. I offered RM1.19, the person counteroffered with RM1.09, and I never ever accepted the smaller offer. Then, economics tells us that sellers will always be willing to sell at a higher price and buyers will always be willing to buy at a lower price. What the hell happened?! Buyers win this battle against the system! I still am holding the can of Coca-Cola that has defied the law of contract law and economics. I did not imply acceptance in any way, but I got a receipt. What happened?!