[QUOTE=Bluemoon Lady;6890910]We had a horrible flight experience with United/Air Canada and Alitalia.

... The return flight was changed by Alitalia in Milan, updated in both the Alitalia system (for MXP-EWR) and the United stystem (for EWR-YYZ).

QUOTE]

I think part of the problem is identified in your first post. You said AZ updated their system and UA's system. That's all good, but apparently they didn't update AC's system, and since you were flying on AC (not UA) it's important their system is updated. Not your responsibility, but my guess is that this contributed to the problem.

Your recourse should be with AZ, since they stickered the ticket and made the changes. I would send a detailed letter, explaining exactly what happened including names of people you spoke with. Stick to the facts, don't exaggerate, include supporting documents, and ask specifically for reimbursement for the UA tickets you purchased.

I don't think you'll have much luck denying charges on your credit card. As far as UA is concerned, you purchased a ticket with them, and flew on the ticket. IMO they will see the AZ ticket as a separate matter.