If your ticket is 160 then CX should fix it. However, i think the afternoon LHR-OSL is already reasonable accommodation. 251 is really restricted for ex-outport inventory, I'm not surprised if they turn you down but you may want to do a waitlist for that (revenue bucket waitlists go through pretty quickly in my experience).

When I look at this and I realize AA EXP hotline/service is still a good benefit sometimes, because if this happens with AA they would probably be able to do almost whatever I want (may take a few HUCAs, but still.) But maybe DMs get this too here.