Note: This public forum indexed by Google and available to everyone on the internet.
We cannot block or delete subscribers from public blogs. Everyone on the internet can view and follow any public blog.
You can change your blog visibility to "private" http://en.support.wordpress.com/settings/privacy-settings/ Please read this about public blogs that become private blogs > Blog Privacy and Subscribers > http://wpcommaven.wordpress.com/2011/09/05/blog-privacy-and-subscribers/
Note that you have complete control over everything that's posted to your blog.
However, if you blacklist be aware that you could be affecting legitimate commenters as well. IP addresses have not been unique for nigh unto 15 years now. ISPs place hundreds of us in the same IP block. Moreover, using the blacklist is useless when people can get a new IP and/or new email address in no time flat.