Not getting what you pay for.

On Sunday night (4th of March '18), my fiancé and I drove through to McDonalds in Brackenfell to get ourselves a milkshake, as I have been craving the strawberry milkshake the whole day long. When we got to McDonalds, I ordered the strawberry milkshake, and my fiancé ordered the peanut butter milkshake. When we got to the window to pay, the lady there that helped us, confirmed again that it was a peanut butter and strawberry milkshake. We got our milkshakes and drove home. As soon as we got home, I realised that I got a chocolate milkshake, instead of a strawberry milkshake. I am very upset because I feel that I paid for the strawberry milkshake, and didn't get what I paid for. I really looked forward to the strawberry milkshake, and don't like the chocolate one.