i called the main number 13 13 13, option 2 - Manage reservations from memory.
On the 2nd attempt, I told them that on the first attempt it told me something wrong with my payment even though during booking, it said the payment went fine and I could indeed see the transaction pending in my credit card.
She put me on hold for a while but I could hear her talking in tagalog with her colleague about 'validation error' or something (I dont understand tagalog).
Then when she came back to me, she said she had raised it with the ticketing team to issue the ticket and asked me to wait for 24-48 hours, and she would monitor it on her end and gave me a call back once she could see it was ticketed.
On the next day (Sat) around 7am I received the e-ticket starting with 081 number, but I got charged again on my credit card with similar amount. In the afternoon, she called me to tell me it had been ticketed (I was surprised she followed up!). She said the initial charge would reverse, which it has.
Good luck! Please share how you go !
P.S. my MU flight is domestic within China, so not sure if it is any different with international flight