Seems to me someone in Australia is passing the buck.
I would have thought that it would be the BA agent in Australia to find your luggage and keep you informed and not wholly up to you to be phoning the UK.
The number they gave you is probably the same number I used earlier this year.I found that it was very hard to get through during daytime in the UK and had best reults in UK evening time.
I would go back to the airport and badger someone there to get on your case.(no pun intended).I found BA good to deal with when mine went walkies.
Hope it turns up, better informed Ppruners shall give you better information I'm sure.