I've been through this exact same thing.
They posted away merrily whilst all the time sending PMs to my members. I didn't ban them initially, due to advice I got from fellow members. They said it would make me appear in a bad light.
So they kept on posting, but I took away their PM rights.
They posted publicly about this, trying to make me look bad. I replied that I had received too many complaints of spam by PM to let this pass. I said that if they behaved, they could have their rights re-instated.
I have never reinstated their PM rights and I don't intend to. Why the hell should I, when they are intent on damaging my site?
I have had to impose short term bans on a couple of them (1 day or 1 week etc.) Usually they come back and complain (publicly), but basically I respond - play by my rules or bugger off!
Their site is failing; schadenfreude is a terrible thing
