The best answer is to ask your lawyer. Failing that take the ad down as you did and reply with a brief "The ad has been removed."

It looks like this person wanted money from you from the start. It could be a pretty ingenious scam too. You put the ad up and then send an email or have a friend send one claiming it is your 15 year old daughter's phone and she was traumatized by a bunch of old perverts talking dirty to her. You're thinking of suing. What will you offer me to make this go away? Rinse and repeat on 1,000 other sites.

Can not be more true. Do never reply on something like that. It will strengten their case and weeken yours.

Getting a lawer is expensive and sometimes worthelss ( they are in it for the money to ) do not do that now.

No matter you cant do anything now, ball is theirs. Wait it out.

If you are not from the same country and they do not have your personal details. They can do wery little and proberly will not.

We can all make threats its esay.

It's good to know as before i would reply but know i wont

Its steve lightspeed trying new business/blackmail ventures.

If you're making so little from the site then I would just shut it down and avoid the risk. For a measly few dollars a month you're assuming a whole lot of necessary risk.

If it's true that you've inadvertently placed the phone number of a 15 year old girl on your site because you've copied ads from the newspaper then you are in the unfortunate position of not being able to claim user submission - you typed the ad from a newspaper and put it on your site. I am guessing the ad on your site outlived the wrong number in the newspaper considering you stated it was from last year.