Especially buying a car. I wouldn't trust ANY online pay system that doesn't track transactions to/from people or yourself, its very easy to send an email as someone else. I could make a rather small script in PHP that will do that.

If you can, cancel the order. Theres not much else you can do, sorry to hear this.

I haven't been scammed, but I've seen enough of it. I especially get a kick out of the African money ones.