I decided to ask the customer service attendant for an explanation and it turned out the pack I picked didn’t have a promotional sticker on it, and they suggested that I just go get another pack with a sticker on, which was pretty stupid in my opinion since all the packs were placed on the same shelf!
Anyway, I’m not posting this to target a specific supermarket but rather to point out that you notice a difference between the shelf price and what you get billed almost everywhere and I’ve experienced it more than once, so you better double check your receipt next time you shop at one of those big supermarkets!