called and did not leave a message, don't know who this is

Calls constantly, leaves no message. Caller ID says Bellsouth.

This number has called me twice today, left no message. When I call back it's busy. iPhone shows its coming from Charlotte, NC.

I have received calls from this number everyday, 3-4 times a day for the past month now! They would stay on the line until the voicemail picks up but never leaves a msg! I recently got another & this ph could ID the number whereas my old ph couldn't! So I googled the number not not much info. But to whomever this number belongs to, I really wish they would stop calling & annoying me!

It's AT&T customer service.
They call when they need an authorization to make changes by anyone other then the account holder for change of service