I have a problem customer who I want to cnacel service on. Can I do so legally if I refund their money?

I own an online live camera streaming company. With our cam we offer a message board. Each customer gets their own thread to discuss what''s n cam. We have a customer whose cam viewers have broken the rules and when reprimanded have created an uproar on our board. When slapped by me (removed posts) they started a Facebook page and are causing issues there now. They don''t openly name my company but they refer to it and me, as the owner, enough that everyone knows who they are discussing. They have posted false accusations, accused us of tampering with their camera everytime it goes down, etc. At this point I would like to shut their cam off, refund their money and leave it at that. I know the flaming will continue but I don''t want the liability of this to get worse. Can I cancel their account and refund their money legally? I have contacted the director of the rescue and she refuses to reply. She posted on Facebook that she fears posting on my forum.