false advertising by McDonalds

On Friday 27th March is saw a street advert by mcdonalds for a R20 mc mixa and decided to go and get it. On arrival i was told there is no such meal. We argyed then decided to go and take a pic of that advert. Te girl said she will spit on the floor we must rush and coe back with the pic before her spit dries. When we returned they looked at it and said that board eas out dated prices went up. I told them its not my problem coz then thats false advertising as i wouldnt have gone there vended up paying more. She told me its not their problem either they wont sell it to me