I didn't realize FT board has become a random rant vent for mere complaints with a strong personal view let alone it be tolerated. So I am surprised it wasn't closed down. Op claims "fraud" on cx part because he/she couldn't get through to agent. Hmm.

Anyway back to topic, there are several ways to get things done. To start perhaps call right after office opens at hk 730am or whenever it was. There is also option on mpc site to change ticket online under "manage my booking" albeit I haven't used this myself or may not have been available. Also for anything that is not a point to point tickets, or of high risk nature with potential changes in itinery, use TA. Exactly for the irregular like this and OP had open jaw. Finally insist - if an agent at Beijing airport cant handle, ask for someone that can.

Bottomline - I always buy ticket online, worked fine on some irregular incidents too. By the way depending on ticket restrictions u might just need to pay no show penalty and use it in future.