According to the BBC today there's a new scam going round involving a brand new top of the range phone.
It's delivered with your name on it, then when your sat wondering if you ordered it or not, the courier returns saying it's been wrongly delivered and can they have it back, you then give it back a week or so later you're stuck with the bill.
Either refuse to hand it back and/or ring the police, unfortunately most "honest" people would just hand it back.
After all you've paid for it {you probably can't figure out how!} but you obviously have.