How to deal with defamation / problem clients

Ok, I'm at my wits end trying to deal with this customer. Basically how it goes. 1. The customer loads funds.

1. 5 minutes later, while we are waiting on the Paypal payment notification he opens a support ticket with payment proof.

2. We reply explaining that funds are in his account and that he needs to order a service.

3. We are then repeatedly accused of being a scam, swore at and genreal rudeness while we repeatedly explain that an order needs to be completed in order to receive a service.

4. Threats to defame and screenshots of posted defamation.

TL;DR how do you deal with false defamation and general problem customers? What experiences like his have you had and how were they resolved?

I would under normal circumstances never post a private support ticket of a user publicly but as you can see he has already done so, violating the implied privacy (although permission I would give willingly) of me and my support staff.

Here are the support replies as proof:

If you wish to say something about my replies feel free to, I don't mind if you have suggestions but bare in mind the thread should be focusing on defamation and problem clients. And please don't say sue.... its LEB people.