I am having severe problems with ad-bots on my wiki

about once a week, or every other week new pages are created that are advertisemetns for . . . I think this shoe company?????

I sent them a message complaining about their advertising practices. And I have deleted, and blocked all of the new users they have created (THEY ARE USING UP GOOD USER NAMES)

This needs to stop . . . I cant stop it I need help for the love of god.