Special items advertised, but not available

I am not normally one to complain and I realize that T&C's apply, but how is it possible that you run a promotion/special on a product and on the second day of the special it is not available? My nearest FLM is 45km from me (that is therefore a 90km return trip). I was highly excited when the promotions from 21 - 27 October included Erythritol (2 x 500g for R100). I decided to drive through this morning in order to get 6 boxes. Unfortunately to my surprise and frustration, there was only one box left on the shelf. I took the box to the till and requested that they please check in the back for more stock, but I was informed that there are no more Erythritol left. I ended up driving 90km to pay R69,99 for 1 box. That is ridiculous and false advertising. If it was the last day that the special was running, it was understandable. I doubt if I will ever go through the effort again. It would've been more of a "special" to just buy it at a local store, even if it was more expensive.