Next time they call have some guy you know with a really deep and tough sounding voice answer and tell em off ;) it always works let em know you are recording the calls and have notified the police. If all else fails have fun with them be as irritating as you want, use funny voices, chew gum loudly, laugh like a evil genius, or just leave them there talking, i could go on all day. enjoy others stupidity!!!
You can get to know the private number that is calling by going to the ATT customer care service office that is near you and lodging this complaint. They will have a record of this number in their database as no mobile phone call can be completed without the mobile carrier seeing the number on their switchboard.
Back when I was a young mother, I was doing baby sitting, with an ad in the paper. I got phone calls from some guy wanting to know if I babysat adults. I asked if he meant mentally disabled or elderly, and he just snickered and hung up. But he kept calling back. I got a toy from my dog and the next time he called I squawked it as loud as it would into the speaker. I never heard from him again.
Having an anonymous caller can be very annoying. I know just how that feels. I've been there.
Your best option would be to keep records of their calls. Date and time, reason of their call and the caller's name if possible.If you don't see the phone number, it's fine. Then refer that to the local authorities and get a police report. Once you have that, you can file for a complaint with your telephone company. The records you have of their calls would help them locate the specific caller and that police report will let them look into the caller's information. It might show as "Private" on your CID, but not on your telephone company's system.
Once you have that callers' identities, you can pursue legal actions against them. And don't forget to report the phone number to the telephone scams watchdog site http://www.callercenter.com.That should warn everyone else about the caller and their phone number.