There have been problems with post being delievered across the country, probably because it is a busy time of year and they are still shifting the backlog from a month or two ago.However, it does sound a little dodgy to me.
How did you send the money, was it cash, cheque, credit card, debit card or an internet transfer?
If it was a cheque, try and put a stop on it, if it was done using a debit card, you can do something called a chargeback-ask your bank about this and do it soon as you only have a limited time to do this. If it was using your credit card, then you can do something called a section 75 request.That is section 75 of the Consumer Credit Act.This means if you have paid for goods not received or that are unfit for purpose, your credit card company will reimburse your account and it is their job to try and recoup the money from whoever took it fraudulently.(Not in this case but if the bank investigate and find you were at fault, they can re-debit the funds).
If it was cash then I don't have a lot of suggestions, as with the internet transfer, as these things aren't covered by your bank.