Hey guys,
looking for some input here on how to best proceed.

We are booked on BKK-DOH-FRA in I-class which used to be a 7.25p evening departure (QR831). Now QR changed the schedule of QR831 making it a 9.05a morning departure leading to a solid 13h layover in DOH. I knew QR had another evening flight so I thought it would be easy to get rebooked to QR833 which departs 9.05p and then still be able to catch my original connection to FRA. Even though QR833 has availability in I-class when booked individually there is only availability in F and Y when trying to book the flight with a connection to Frankfurt. See below:

Looking up BKK-FRA:

Looking up the legs individually:
I called QR 2 times, once their international line, once the German line. Both with the same outcome.
German line agent flat out told me that he agrees that there are seats available but the system does not let him rebook me to that flight. He suggested I go to DUS or MUC where he could rebook me on QR833. I told him I already have a seat from DOH to FRA, I just want BKK-DOH on QR833 which evidently has seats open in business. Asked for the supervisor, said that he would't come in until late today.

Second call to the international line had the same outcome. Acknowledged there are seats, then told me she cannot rebook me as the connection time was too short. Told her they are selling the same connection in Y and F. Then told me it is a marketing decision (that's probably right). When I pushed further she went back to telling me there are no seats open.

So, I know there are seats available. I want an evening departure out of BKK but QRs system won't let me rebook to it. Any idea how to best game the phone agents? I feel like I am talking to a brick wall.

Regards and thanks!