@kate - just prompt Aus Post again via message.

One of the main issues it if the seller actually sent it with SOD, regardless of what any message on the packaging said. Aus Post can tell you exactly what type of postage was purchased.

So, if the seller didn't send SOD (required with anything valued over $750), then I'm not sure what the next step will be as tracking shows delivered. You might have to open a case for Not Received, but in the notes you can mention that it was not sent SOD as confirmed with Australia Post.