product adverti*****t lie

Ordered a Chilli cheese meal at McDonald's Avonwood tel ***. They didn't have cool drink that comes with a meal and asked if I would like a juice or shake. I chose a shake. But I end up paying the whole meals price of R39,90 without a drink and extra R12,00 for the shake. Meaning i lose out on a cool drink. I asked why they do that they couldn't answer me. Their service is pathetic. They need to have system on place when they run out of soft drinks.