Big Mac Burger made incorrectly but was told im wr

I took my family of 4 kids and Wife to MacDonalds in Milnerton, ordered some food and ice creams for the kids, one of the burgers I ordered was a Big Mac, same burger i eat every time i'm there. when i opened the burger it had nothing between the Middle bun and top bun.. not even lettuce or mayo... when i approached the Manager on duty, i was told that that's how big Macs have always been made, i tried to argue and one of the cashiers mentioned that they will \fix"it"