Who called from 6152650014

I received a call from this unrecognized number at 9:51 AM EDT. The caller ID was "NAD". I did not respond. The caller left no voicemail.

I received another call from this number at 9:36 AM EDT. The caller ID was "NAD". I did not respond. The caller left no voicemail.

i picked up and no one there

Calls nearly every day, sometimes multiple times a day. When answered, they hang up after our standard greeting (we are a business) and when left, there is no voicemail. Caller ID shows NAD.

Received call from this number, could hear people talking in background but nobody spoke to me and the caller hung up!