I booked premium economy on AF website (AF operated, AF marketed) and am trying to use my GUCs to upgrade to Z. I’m not sure if it’s because I’m getting the weekend crew, but the (Diamond) phone and chat reps have all told me they can’t apply GUCs if Delta didn’t sell me the ticket. They’ve directed me to call AF. I’ve copied/read aloud the GUC T&Cs which obviously contradict their claims, but they won’t even try to help. What magic words do I need to say to even get them to do this? (I know the Z inventory is there for the whole trip per Expert Flyer).