Are you sure you didn't purchase a pre-order?
If you purchased a pre-order, you will receive an email when your pre-order is available for download. You cannot download it before the release date.
Make sure you are logged in with the correct account!
This may sound stupid, but it can happen!
Make sure you try logging in both with Facebook and with your email, as they are separate accounts (unless you have merged them).
If you made your purchase by logging in with Facebook, you need to login with Facebook again to retrieve your downloads. Similarly if you logged in with your email and password, you need to login with email and password to retrieve your downloads.