Did I Really Win The Money?

Its most likely a scam, you need to burn that letter or throw it away and if they ask you money for something or some sort of shipment, just ignore it and walk away. In life if something is too good to be true, it usually is. Its just a lame attempt at separating you from your hard earned cash and precious sanity.

Did you enter a competition where that is the prize? Its extremely unlikely to be anything other than a con

If you were not expecting to win anything then the biggest chance here is that its a scam when you do contact them it will be a really expensive phoneline rate and they will want you to register for a clothes catalogue or something very similar be wise bin it today