Calls but never leaves a message

I just got a call from this number.  I let it go to voicemail and of course no message was left.  I've been getting a lot of these calls lately with local area codes but they just hang up if I do answer.

Yes this number call quite often and does not leave a message. Maybe it has something to do with a survey...

Said they were calling from some "Smart" something-company about my Washington Gas bill.  Said they don't know how they got my number.  When I said to remove my number and I'm not interested, they just hung up.  They are probably affiliated with the other phantom numbers that keep calling me like 301-937-6784 because when you call back the calls never go through.

Got called from them too.  Said his name was "Emanuel" calling from Washington Gas or maybe something related, he started mumbling.  He had a heavy accent and said he wanted me to authorize discounts on my bill and to give him my account number.  When I said I didn't have it and wasn't home he said to go to a computer and look it up. When I said I couldn't he said he would transfer me to Washington Gas to get it.  Needless to say he was very intent on getting my account number.  Definitely seems like something fishy, recommend not to answer this one.