Blog notifications for the admin (like comment moderation, Likes, new subscriptions, etc) are sent to the email address at Settings -> General in the Dashboard.

Personal notifications (like comments on your post, subscription emails, and upgrade renewals) are sent to the email address at Users -> Personal Settings in the Dashboard.

If you did not change your email address do not click the link in the email you received. If you think your blog has been hacked read on.

Go to your email program and change the password to a very difficult one because that's how many hackers gain access to blogs
Then read this please knowing that blogs don't get hacked when security protocols are followed. > http://en.support.wordpress.com/security/

1. If you can log-in go here > Users > All Users and delete any user that does not belong there.

2. Disable post by email > http://en.support.wordpress.com/post-by-email/

3. Disable post by voice > http://en.support.wordpress.com/post-by-voice/

4. Change your blog password to a very difficult one > http://en.support.wordpress.com/passwords/#change-your-password

5. Use a secure, encrypted connection to connect to your Dashboard. Under Users → Personal Settings, check the box that says “Always use HTTPS when visiting administration pages, and click Save Changes.