CID says "Cell Phone" but call was intercepted as a robo-caller.

do not know anyone from area code 571.  did not pick up.

I've received several calls from this number recently but I didn't answer.  I called it back today and it was answered by a recording that said the mailbox was full.  At the end of the recording a guy stated his name, but I couldn't make out what he said nor could my husband.  I'm just going to block this #.