Vietnam Airlines had overbooked the flight so I was changed to a Thai Airways flight at the last minute, so what should have been a direct 8 hour flight from Melb to Ho Chi Minh turned out to be a 17 hour travel from Melb - Sydney - Bangkok - Ho Chi Minh City.
Had the same trouble coming back, couldnt confirm my ticket, the booking had been cancelled due to overbooking by Vietnam Airlines again! After several hours of arguing at the Vietnam Airlines head office and calls to and from my travel agent in Australia, I got upgraded to business class and was able to fly back on the correct date. My mum and aunt who were supposed to be on the same flight as me got put to a different flight from Ho Chi Minh City - Japan - Cairnes - Sydney - Melbourne. They were at the airport in Japan for 14 hours.
The actual service on the plane, food etc on Vietnam airlines is ok, but the overbooking of the flights is just unacceptable. People pay good money for the flight so should not have to stress out about whether they will get home on time or not, and we shouldnt be sent all around the world when we purchase a direct flight. I will never travel Vietnam Airlines again and suggest people reconsider booking with them, especially around peak season because I know it wasnt just me in this situation.