Final Update: Got a phone call from HN PN store owner, explaining that he was very sorry and that he didn't have all the information when he wrote the letter. He kindly offered me the usb version of the anti-virus for free, which was really decent and which I declined as all I wanted was an apology. He mentioned that the staff member in question got an official telling off too, which I think was totally warned because of his lies.
So thanks to Harvey Norman for sorting this issue out and taking steps to prevent this from happening to other customers. A big thanks to http://twitter.com/harveynormannz for helping to prod the right people. Awesome value from the social engine.