I am not sure if the trick works for booking ex-Australia, but the trick commonly suggested on Flyertalk (at least for ex-SIN bookings) is to dial the Singapore number and press 2 for Mandarin. Tends to get you to a call centre with greater competence/freedom (in Singapore, where most speak mandarin and English). Haven't tried it myself though.
Is you booking BNE-SIN on a separate booking? If so, whatever carrier you choose will not take that into account if they change their schedule, you or your insurer take that risk.