If you haven't already sorted this, or if others need to know:
- go to your profile page (login, then click on your journal's name on the top bar, then select "My profile")
- click on the word "Followers" (in a box above your recent entries)
- to the right, above the followers shown, click on the word "Manage"
- this will give your followers in more of a list format, along with a "Remove" button close to each of them
- remove the unwanted individual(s)!
I don't know if that prevents them from following you again. But if they were to try again, I'd be tempted to notify Blip Central of any such harassment - if that's how you consider it.
Hope that helps!
Some feedback can be helpful for others to know if it did or didn't work.