how to stop new user registration email for multisite set up

When ever we use batch create the new blog is set up, but the users gets two sets of logins.

the first is to the main blog, the second is to their own personal blog. The issue is that its confusing our users. We only need to send them their personal blog login details, not their user details for the main blog.

We have tried to disable this email message in the settings, but it keeps sending, how can we stop this email?