Buy 3 and pay for only 2 ****

Bought their "buy 3 and pay for 2 only" special on their Bobtail dogfood and received only 2 bags. They were conveniently out of stock so I received only 2 bags which I paid for! Surely they should've have made sure I received the 3rd bag as soon as stock was replenished? After numerous emails to them the contact agent rep**** but they only CHARGED ME FOR 2 BAGS AND NOT 3! This is just a **** to get people to buy more than they intended because I would and never would buy 3 bags of dogfood at once. I only did it because of the "special". I wonder how many customers fell for this trick