My blog is being spammed

I have a Plesk blog page, but I'm regularly spammed with this kind of comment:

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etc,

I spend time to clean up every day and its annoying.

The no.1 traffic on my site comes from unassigned.psychz.net by a huge margin. I was wondering if I could stop the traffic from this site, see if that is what is causing this spam problem.

Thanks for your help,

Andrew