Ouch. Were you flying without any status at all and using DL agents in the regular (ticket purchase or check in???) line? I assume this was a discounted coach ticket. Still, $2800 sounds like it could have been a buy-up to full Y (or at least B) which could technically be correct if this was your (first) outbound flight on the ticket. Did the people you talked to explain anything about how they were doing the price calculation?