Their phone system is a joke. For days I've call the 800 number in the US and any option I select either disconnects me, gives me someone's direct voicemail or rings endlessly.

I finally chose the option "New ticket sales" and was routed to a woman in Turkey, or at least Europe based on the ring, and got the ticket change and seat assignments I wanted. Forget going to the existing reservations / changes options, they'll fail you.