Several of my clients contact me monthly, complaining about getting debt collection calls from payday loan debt collectors, that they either never took out, or that they had many years before they filed bankruptcy. Some of these collectors threaten my clients with jail, tell them that they are filing a lawsuit against them and that the sheriff will come to their job that same afternoon, other nonsense like that.
As this video below indicates, there are some of these people that are just "off the reservation," and I mean literally, they are offshore, in another country, and not in a place where we can really do anything about them.
If they are calling you and they are not real (the video explains how to tell), just ignore them, or if you want to take action, complain to government agencies.
If they are real debt collectors and they are violating the automatic stay of bankruptcy, of course contact my office and we will sue them in Bankruptcy Court. Same thing if you have your discharge in bankruptcy already, or if it is a "real" debt collector that is violating the law by illegally threatening you, or abusing or oppressing you.
But if they are one of these "renegade" fake debt collectors calling you from who-knows-where, suing them wouldn't do any good. There would be no one to serve with papers, and no way to collect a money judgment, if we were able to get one against them. The FTC recently shut some down, but there are more.