The team leader of the call centre called me back, with no new information.

I rang HBA and MBF on the off chance they would cover us if we transferred cover and miracle of miracles they both said they would and the premiums are cheaper! I'll go into a branch and get it all in writing before cancelling with AU, but big relief that we finally have some options. My dh is keen to quickly get to the dentist and physio before we cancel just to make sure we claim as much as possible from them.