I have always found Australia Post very helpful.  

Maybe if you get someone who isn't helpful, ring back and see if you get someone better 🙂  

I had a lost parcel last year, (parcel post, no tracking).   I got the number of the PO where it should have been delivered from.   They rang me back next day to tell me the parcel was still at their office !!   and would deliver it the next day .... same thing with another, and they suggested the buyer come to the PO and pick it up !!!  I didn't ask questions .... just glad they were found.  

Not to mention the phone call I had from NZ one night .... A/P had put parcel in wrong letter box in Queensland,   house was being rented ... owner lived in NZ.   Renters sent the mail off to owner in NZ.

BUT .... the 3 parcels were actually received by the seller in the end  🙂

Happy endings 🙂