Unfortunately, this seems to be a scam!
I purchased my 950XL between Christmas & New Year. I got the offer details and personal code and followed the instructions. I received an order confirmation and thought no more about it as the delivery was supposed to be in 12-14 weeks. The next thing I know, a couple of weeks ago, there was suddenly a pending transaction against my bank account for the full price of the Display Dock. I rang Microsoft and then sent them both the E-Mail containing the offer code etc. and the order confirmation. I was given a reference and promised that the matter would be resolved within 72 hours. That was on 19th February and whilst the pending transaction has since disappeared, I've heard absolutely nothing from Microsoft despite a reminder! I shall be trying again shortly and if I still get no response, I'll be reporting Microsoft to Trading Standards (or whomsoever deals with this sort of thing) as I'm sure making an offer like this and then not delivering is unlawful (in the UK anyway).
Don't get your hopes up but watch the account you gave details of when you ordered very carefully!