So here's my situation - I flew from JFK-DUS a few weeks ago on AB for last minute business. I checked in online the day before, and being 6'5" tall, I was going to pay out of pocket for a seat with greater legroom. I had two options in row 36 - the Preferred seat by the door, 36A (54 EUR), or the XL seat next to it, 36B (85 EUR). I paid the 54 EUR, thinking I could deal with the encroachment from the door. Once on board, I found the exit door was far more intrusive than expected, and I couldn't sit comfortably without resting my legs on the passenger next to me. During taxi, I noticed the XL seat across the aisle was open, so I asked the FA if I could switch after takeoff. She said I could, but I'd have to pay. I understood that, however I told her I had already paid for my current seat so I asked if I would only be charged the difference. I even showed her my original invoice. She wasn't sure, but she allowed me to switch and said she would figure it out with the purser.

Anyways, I switch seats and go about enjoying the flight. A couple of hours or so before landing the FA's come to process all the charges, and she says she has to charge me the full 85 EUR. At this point I'm tired, and I figure I'd rather argue with corporate than with the FA on the plane.

Well you can see where this is going - I've had two rounds of emails, and I've called AB customer service, and I keep getting denied. I just want a refund of the 54EUR I paid originally, since I also paid the 85EUR for the XL seat. When the FA let me switch, she said she was unsure of the rules and was surprised I even had to pay for my original seat, 36A.

Am I being unreasonable, and if not, what's the best way to escalate this?

Also, I should note that AB lost my luggage for 3 days (suits and all) and I'm fighting a separate battle to pay for the socks and underwear I had to buy for my meetings, but that's a separate story.