(I'll write this as a weird roleplay scenario.)
You'll walk into the KFC and go to the counter, (or the drive thru.)
"Hello, excuse me?" You'll wait for someone to notice you and take your order.
"Hello, what would you like today?"
You: "Oh, no, I just ordered not too long ago and when I looked through my food I noticed it wasn't what I ordered. I'm not too sure if you accidentally gave me the wrong order or something was messed up."
Patiently waiting, the counter man/woman would most likely nod and take the bag, asking for a receipt.
"I'm sorry for the inconvenience, please wait a moment as we fix this and we'll be right with you momentarily."
(That's how I feel it would go! Hope that was something.)