Login to My Account as a Returning User.  If you see a silver tab at the bottom of the Subscription Products box that says Enable No Hassle Billing – it is not Enabled and will not auto renew.

If you do not see one, you can click on the blue link within the box that states, Turn off No Hassle Billing or Update credit card details.  Once you click this you will have an option to Cancel No Hassle Billing.  After clicking this, verify that the silver tab is there stating Enable No Hassle Billing.