Who called from 5132343046

They say they're attempting to collect a debt but they don't have all your information

I keep getting calls but no message, I do not answer calls when I don't recognize the number. These are coming to my cell phone.

These people have called my cell phone and now my work phone. They have asked my coworkers if they knew how to get ahold of me and also left a number to call saying it was "Mike from ATC." They are trying to collect a defaulted student loan and do not ask for any information to verify who I am. I answered once because I was at work, but I don't think they are legit so I haven't answered since. They keep calling multiple numbers at my work and my cell phone. Any suggestions?