When you booked this flight, the HKG-SGN leg was originally going to be operated with a 2-cabin (no F) aircraft, right? So you were booked into J for that leg? Was your ticket also a biz fare class for that leg?
If so, I get why you feel like you should have gotten upgraded once the equipment change occurred. BUT, they didn't owe you an upgrade, they just owed you what you paid for.
Anyway, I apologize if I misunderstand any of the facts.