Originally Posted by IanFromHKG

Call back, ask for written confirmation (which may not be forthcoming) and as a fallback ask for their names, make a detailed note of the conversation, and be prepared to argue your case at check-in. But don't volunteer information about it when you check in, just check it in, and if they start asking questions, only THEN do you raise the "I asked MPC and they said it was fine" discussion

Good luck!