I’ve had similar issues with BA Silver OWS number on an iberia booking. Called up last week for one reservation and also got told to “tell them at the airport what seat you want to sit in”!? And this was after he spoke to a supervisor…!
A tweak to the work around that’s been discussed before:
1. Make booking on iberia.com and add FF during process. Rarely this is enough to be allowed free seat selection. Booking email received with 5 digit reservation code.
2. Call iberia and ask for the 6 digit Amadeus code (every iberia reservation has 2 codes for 2 different systems - I don’t know why). You can explain it’s for a known work around to select seats - a problem that’s at least 6m old.
3. Login to the iberia manage my booking with the new 6 digit code. The reservation is the same/identical - but it probably won’t have your frequent flyer number saved on this side. Add FF number to booking - and see if you can select seats - this usually still doesn’t allow free selection.
4. Now go to oneworld member rj.com . Login to MMB here using the 6 digit code - click on seat map and you should now be able to select a seat for free. Save that and close.
5. Login to iberia MMB with either code and you should now see your selected seat saved. Sometimes it’s only visible for me on one side, but usually both. Rj.com method works about 90% of the time for me. Ps. I wouldn’t mention to iberia that you want the 6 digit code for rj.com - just say for their website to select seats.
Unfortunately this didn't entirely work for me. I was able to bring up my reservation on rj.com. Made seat selections but they didn't stick and I did get an error on that site. It seemed to save 2 of 4 flights, and seats for me only (not companions) became reserved. On Twitter, Iberia finally responded to me and said they checked with AA/OW, and only I am eligible for a free seat assignment (not my companions on the same reservation). Above, a poster quoted the Iberia website, "Clientes con tarjetas Iberia Singular, Iberia Plus Platino y Oro (esmeralda y zafiro de oneworld) podrán seleccionar de forma gratuita el asiento desde el momento de realizar la reserva, para todas las personas que figuren en la misma reserva." But it seems this has been removed:
https://www.iberia.com/es/reserva-de-asientos/. What a frustrating experience. With all the stories of oversold slights and pax getting bumped, I might just shell out the $$ to reserve the rest of the seats, ugh.