If it is a debt collector they are required BY LAW (15 USC 1601) to annouce who they are, who the company they are calling from is, that this is an attempt to collect a debt and who they are attempting to reach. They cannot reveal any other information unless they are speaking to the person in question but they can and must give the above information. If the initial message is threatening arrest or other action, it is all but certain to be an illegal attempt to collect a zombie debt or an outright scam as being reported by the FTC and other authorities.
In addition, any legitimate business or individual will leave identifying information as to both who they are calling and who they are. If they cannot do that, they do not deserve any calls back. In addition, even for calls of a sensitive personal nature there are ways to provide enough information to determine if the call is legitimate or not without revealing protected information.
These people are relentless. They change their name to avoid being found. They also change their phone numbers, and also Spoof numbers on your caller ID. Real Low Life. Here's the lay of the land as they say, I work in the court system so I will go thru this for you .
First they are calling because they say they can not find you. This is Crap as the sheriff, will NEVER, EVER call you to tell you they are coming. They live to work on the element of surprise. Plus if your township, county etc, wants you, they already know where you are, so sit tight.
Second, and most important, NEVER CALL these low life bottom feeders back. Because truth be known they don't care who they talk to as long as they can get money from someone. It doesn't even have to be the right person. If you call them back then they know that they have a real tangible working phone number that they can call to harass you all the time of day and night. Just ignore the call, or better yet, tag them as a spam call in your phone, and you'll never even see them ring it.
Third, these people function and live on the *Fear factor* they will say anything, tell you anything to get you to give them the money thru your checking account, debit card or credit card. Many people get scammed this way. I've heard : coming to your workplace to arrest you, serving you in the morning if you don't call by a certain time, attaching your salary, etc, etc, this is all nothing but crap.
Fourth, in most states payday loans are ILLEGAL as they charge obnoxious interest, and states are trying desperately to control that. Since I'm not sure of what state anyone is in, I cannot site them all here, but if you go to your states attorney general page, you should be able to look up the laws.
Fifth, I know it sounds nice to send them a letter or report them, but this is a futile. They have got this to a science. With all that is going on in court system they know they have time on their side. Not enough of these low life bottom feeders get caught and prosecuted, if they did...they wouldn't still be in business, but they are, thousands of them.
Lastly, anyone who posts that you are scum or a deadbeat PAY YOUR BILLS , OR OMG they came to my place of work and arrested me, are full of crap and are just trying to SCARE you, SEE MY THIRD NOTE Above, Fear factor.
Best thing to do in this case, especially with these people is TO IGNORE. Eventually when no one engages with them they will go away to torment someone else.