In my opinion if warnings are not heeded then a ban, temporarily at first should be of the order.
I know other websites which have had paying users post alongside visitors where this is the case.. Bans first were 1 month, then for repeat offenders, 2 months, then 3 months. Most learnt quite quickly that their bullying and aggressive antics were not welcome and the forums became a better place.
I’m more of a lurker now popping in rarely to see whats about. I simply don’t have the time to read through pages and pages of forum postings (as well as getting 1 email for each) to try and find something that is of value and on topic as opposed to a petty battle.