Trying to buy exit row seat - payment fails but credit card is charged
 

I know TK's website is the worst in the world (together with Hertz's), but I tried selecting exit row seats for a flight in June.

I am willing to pay the 79 USD they're asking, enter my credit card details, and get an error saying payment failed. Yet I see from my bank's website that the card was authorized (and later even charged). A few days later an automatic refund took place. I've tried three different credit cards, all of them fail in the same way (2 Visa, 1 Amex).

I also called their callcenter, they're running into the exact same issue, they're blaming my banks, but I can clearly see the charge are successful, and Amex confirmed that the authorization was approved by them.

I've been told to go to a TK sales office, to which I replied that I thought it was 2017.

Short of actually going to a TK sales office, any other clues as to how to resolve this and get an exit row seat booked?