Just contact their Customer Support now and you'll get an answer back soon. Amazon is a good company. Look in the Accounts section and you'll find how to cancel the order and how to contact them about it.
Go to your Amazon account page and check under "my orders" if there is really a order that you didn`t make. If there is, change your password immediately! Use a safe password, containing a dozen letters and numbers, upper and lower case. And contact customer support and tell them about the order and cancel it.