Easy answer to such calls is “Either identify yourself and provide me with a written legal document (and no I’m not giving you my address, if you got my phone number and are actually an attorney, you can figure it out on your own) or go completely fuck yourself. Never call me again or I’ll be calling the police and filing a harassment complaint against you. GOOD DAY!”
Anyway, you’ve got three separate questions going on here:
Is Random Nameless Phone-Numberless Dude in fact a lawyer?
I highly doubt this. A lawyer would’ve sent you a snotty letter or at least an email, on letterhead, in full legalese. Not rung you up and said ‘I am Lawyer X with no phone number or law firm and you defamatised my, um, clientelerie.’
Have you committed defamation?
No way for us to know without knowing what you said.
Should you take the post down?
If you said anything that wasn’t true, then yes, whether it’s defamation or not, you should take it down. If everything you said was demonstrably true, and that’s a defense against defamation where you are, then personally I’d leave it up.
If what you said about the poster was true and provable, you should be on firm legal ground.
Real lawyers generally identify themselves by name and are not unwilling to provide you with contact information. They are likely to communicate with you by registered letter if they are requesting that you do something, so you cannot deny receiving their communication.
So a person that has committed a serious crime has become angry with you, blames you for their inability to find employment, and knows your real name and phone number. Your address will probably be even easier for this vindictive criminal with poor judgment to find.
A guy with no job can afford to sue people for talking online about his criminal past?
I have to wonder why an attorney would take such a case. The client shouldn’t have any money and what are they going to collect from suing?
When they say they are a lawyer maybe it’s the kind that is a fish.