I got few call from this number, only silence, no msgs

I got a call today on that number also..and when I dialed back it says number disconnected, then I also got an email for no specified sender..? wonder if they are connected in anyway?????

Called tonight - person identified himself by name and said was calling from Federal Collections. (I told him I wasn't home.)

I got it as well, today, silence.

I have been getting calls from this number for a week now, and they never leave messages. They always call in the mornings