I booked US <-> Spain flight through booking.com for a Finnair flight which is operated by Iberia and AA via codeshare. I had no problem picking our seats on AA. Iberia has been a complete NIGHTMARE:

I can pick Iberia flight seats, and pay for them via my credit card, and my credit card transactions show the Iberia charge. But when I go back in again to view the flight it says payment due for those seats. So I enter credit card again and same thing happens! I wait two day and try again -- now it shows I have NO seats reserved any Iberia flight. So I pick seats and enter credit card again. Now I get "an error has occurred. Payment context not found"... I try this 3 times during a day and same error.

Over past few days I have had 3 long phone conversations with Iberia, and later long chat conversations( so I have a written record). I get a different story each time.... most recent answer in chat was :

[1/13, 12:08 PM] Iberia: In this case, for a shared code reservation, as is yours, the assignment of seats can only be done through the website. If it does not work on the website, it must be done at the airport, where our staff will help you. With the process.
[1/13, 12:09 PM] Iberia: The website generates errors when booking with shared code, we are very sorry for the situation and we are improving on it.
[1/13, 12:09 PM] Iberia: In this case, if any charge was generated, it will be returned automatically.
[1/13, 12:13 PM] Iberia: Even though they are Iberia flights, the ticket belongs to another airline, which does not allow us to assign the seats.

So the Iberia agent said cannot pick seats for me now via phone or chat. I have I have to wait until I show up at airport months later on the day of the flights to pick our seats!

Anyone else having this problem? Any idea what to do? Can I get my money back on this non-refundable flex flight booking... maybe via a credit card company chargeback?

Calls to Iberia, Finnair, and booking.com has resulted in no solution.