Update: No refund yet. I phoned AMEX Australia earlier this week to request chargeback. They said airline tickets always take a minimum of 6-8 weeks for a credit to post on the account. They advised I need to hold off on a chargeback until 8 weeks have passed. Not the advice I wanted to hear, but not much else I can do at the moment. I imagine they can see how slow airlines are (purposely) being to hang onto their cash as long as possible. Not ideal for the consumer!