Mushroom Swiss Chicken Burger?

Sometimes you just want a burger and fries. I found out that McDonald's has starting serving the Mushroom Swiss burger again. I like this burger and was craving it so I had to get one before they stopped serving it. I went through the drive-thru to get the Mushroom Swiss Burger Meal. When I finally got to the order speaker, there was a note on it saying that they had no beef patties available. I didn't quite comprehend it when I said, "Can I please order a Mushroom Swiss Burger Meal?" The voice on the other side apologized and said they didn't have any beef patties. The voice said that they did have chicken, grilled or crispy, that they could use instead of the beef patty if I wanted. I was already in the drive-thru line with no way of getting out and I was hungry. I agreed and ordered the grilled chicken. So essentially it would be a Mushroom Swiss Grilled Chicken Sandwich. Didn't sound too bad. Then after I paid for the meal and went to the pickup window the server apologized and said that they didn't have grilled chicken. A little stunned, confused and irritated I said that I'd take the crispy chicken instead. I finally got the meal, drove home, opened the bag and took out the sandwich. Surprise again! It had a grilled chicken in it. No. 1, how does a McDonald's run out of beef patties? No. 2, why do you tell a customer you don't have something, give her little choice to order something else, tell her you don't have that something else, then serve her that something else that you said you didn't have?