The person you spoke to might not know, but if you really did get passed over for the upgrade by someone with lower status CO Insider will be able to look at the details of your ticket and get an answer from the people who can figure it out.

For clarification, AU is the immediate upgrade for elites on a Y fare. EUA is the free upgrade based on status levels that happens 5/3/1 days prior to departure. It sounds like the latter failed for you, not the former.