Special not so special!

Good day My coleague and I went to buy Steers ribster meals, only after paying we noticed that it comes with a shake for R10 as an addition, when asked the guy at the till to please add it on our meals he refused as we already paid, but I don't see how because the meals where not even prepared yet, we were still at the till, I felt its being a ***** of some sort, I also feel that he should have also advised of the shake as we didn't see it, if that's how steers treats their customers then i'm never buying any specials again. the burgers had small meat in the middle with a lot of source around the bun, it should actually be called the sourcy speacial