just my unsolicited two cents.
this is not peculiar to Avianca, but common to most (if not all) Star-alliance airlines.

1. an upgrade ticket will usually book into an upgrade fare bucket, not a straight up revenue bucket. you only get credited for the original fare bucket in economy. you likely can try to retro-claim again to Asian and explain that this is an upgraded ticket, and you want to retro-claim the original economy ticket booking code.

2. Considering the person(s) you were talking to were likely not English native speakers, the wording of your question was vague and likely misinterpreted.
"find out what class the ticket would book under." --> answer is, straight up paid biz class is in D.

But your ticket was an upgraded ticket, so the correct question could have been.
"find out what class the ticket would book into AFTER UPGRADING from economy class to business class."

3. not adding salt, but you missed the double check for ticket number, fare bucket, booking code etc. basics of basics in the miles game if you really want to accumulate the miles. lots of tools out there, including https://classic.checkmytrip.com/