Tracked my packaged from NSW and it was marked "delivered" but I don't have it?

I bought this item off ebay a few weeks ago, seller is from Australia and posted it the day after I paid and provided a tracking number. I've been tracking it since they posted it, and yesterday it said "with Australia Post for delivery today" I was home all day with no package arrival (no one came, I checked the CCTV) and then my tracking info said it had been delivered.. but in Welshpool and I live in Como. I assumed it was going to be delivered today as the distribution center is in Welshpool and perhaps yesterday was a busy day, but nothing arrived today.

Has anyone had this issue before? Who should I contact?

Here's a screenshot of the tracking details http://imgur.com/L5imvMI