I had similar problems re-booking two MH flights, with the call center being less than helpful, much of it due to lack of training and lack of empowerment to make any decisions. I got a (somewhat better) response by sending a polite, but formal and firm email, requesting a response - and got a call from a more senior & knowledgeable staff member.
If you haven't received an email/website confirmation of your new flights, I'd call back to confirm and get written confirmation - it might not have gotten approved/ticketed...