Thanks for posting. How much I loathe these kind of 'technical' support desks, who in the end have no clue what they are talking about..
In what way were you expecting this to work? If the flights had no availability in Y class, it would not have been possible to book with the Flight Bundle either, no? Or did you get a Business flight bundle (if that exists)?
Perhaps that message was popping up because the flights are sold out - have you tried different dates with better availability?