I had to go to the Post Office again today - more packages to NZ.
The lady at the counter was the one from outside, yesterday morning, and, recognising me, asked if I had recieved her message? To which I had to reply: I gave her the incorrect number... So she turns away, and from behind the counter gets a plastic bag...
O - M - G
It was there!
It was there!
It was there!
So now I just feel generally daft - but relieved. 
And my flatmate is vindicated: he told me that my iPod would have been handed in because (and I quote) "people who use post offices are more honest than the general public."
