Since my original post this morning, I spoke to Australia post and the agent said that the parcel was officially delayed so she advised that I open a customer enquiry. She also asked whether I had been in touch with the buyer to ask whether they had actually received the parcel and I did that after talking to her.

The buyer told me that they had received the item and that no, the postman had NOT asked them to sign for it, despite the fact that I paid for registration of the parcel.

This is the explanation for why there was no updating of the tracking. When I spoke to the Australia Post agent again, she said that since the signature of the recipient was not obtained by the postman, I would receive a refund of the postage.

That's good, but I would have preferred delivery confirmation. That's the primary reason I get registration for my sale items !!