The first sector of my LATAM business class flight GRU/SCL/SYD (booked with Avios through BA) has just been cancelled and rebooked on an Economy only flight GRU/SCL. According to BA res in UK, I should retain the Business class baggage allowance for the entire journey under IATA "Most Significant Carrier" rules for mixed cabin connecting flights on a single ticket.
However I have just received a reply to my online query to LATAM customer support advising that I only have the economy allowance on this sector. I'm trying to avoid the predictable argument at GRU check-in so does anyone have a link to the relevant rules?
I'm particularly concerned as this is an involuntary downgrade and I've been told by BA that they can't change me to an earlier GRU/SCL flight with Business Class (currently showing available) without first cancelling the whole booking as these are "married sectors". Shouldn't LATAM have offered this as an option?