an interesting thing happened recently to me, and I believe it may be linked to this sort of ad.
Got a call over whatsapp from a number i didnt know. Didnt answer it, then got a text saying 'call me back, I'm on my way to sheffield'. They called again and I answered, to be greeted by a man with an eastern european accent saying he'd just got out of jail and was told that I'd been messing his girls about and he was coming to sheffield to collect payment for the waste of time, and if i didnt pay he'd come to stab me.
He had no other info apart from the sheffield location, and his number does not work if I call normally, only over whatsapp. So I reckon they use the ads to collect numbers in different cities and then call them to see if they get any bites. I can imagine some people would be pretty shook up by someone making those sort of threats and may pay to keep them away. With enough numbers it could be pretty lucrative for them.
Anyway. Always use a punting phone and never give personal info.