First time flying AA and it may just be the last!

Have a couple of flights booked on the same PNR for later this month. Decided to buy Main Cabin Extra seating, selected seats for both flights, AA.com only processed my seat request for one of the two flights - email receipt indicates only one charge, but when it posts to my credit card a few days later it appears I was charged for both regardless.

I've since done a second transaction on AA.com to buy Main Cabin Extra for the second flight, so ultimately they've charged me twice for the same transaction.

@AmericanAir on Twitter says "We're showing that the charges are correct" and wants me to write to CS if I disagree, so I suppose entering a dispute with VISA is probably the best way to go here. Probably better to wait until after the flight to start a dispute, I'd imagine...

Do any of you AA flyers have a better suggestion? I don't know how well AA deals with written complaints, but in my experience with other airlines, i'd prefer not to write to customer service as it would likely take them longer to respond than I have to file a dispute with VISA.