Its a scam.   You can't win a contest you didn't enter.

The way it works, when you call they'll ask you for your bank account number so they can deposit the money.  But they won't deposit any money.  They'll take all of your money out of the account.  OR they'll ask for credit card information and spend you to and over your limit.  Or they'll find some other way to steal your money.  After they have your money they'll vanish and you won't be able to find them.  You'll never get any money back from them.