I was in Turkey, paying for some groceries, my Turkish was way too rudimentary, and the cashier didn’t seem to speak other languages. When I did not understand something she said, she repeated the exact same thing, only louder. I still had no idea what she was saying. There was absolutely no problem – I had paid, my wallet was in my hand, not on the floor, all the products were in the bag… And she kept repeating the thing she said before, louder and louder, as if she was expecting something from me. I looked puzzled, and tried to communicate using other languages, gestures, trying to guess, playing mime. She finally understood I was clueless about what she was saying, and, almost yelling, she repeated that same thing one last time, grabbed my hand, took some coins, gave me a banknote, and then (thankfully) ignored me. Oh… so she needed change. Pointing to the coins would have worked like a charm.
Moral of the story: shouting the same thing louder won’t make you understood; adjusting your message does the trick.