Misleading advertising

Makro advertised a special: if you ordered 6 x 750ml bottles of Meerlust Red wine you'd get a magnum free. I ordered online. Delivery was only the 6 x 750ml bottles - no magnum. Upon inquiry I was advised: "the Amanzimtoti store informed us that you did not include the deal on the website". However, there was no "choice" on the website to include or exclude the deal when I ordered. And anyway, why would anyone ordering the 6 bottles not want a free magnum?!!