Its one of many numbers over the past few months coming out of Maryland from the same people claiming to be Washington Gas, and saying either there is past due amounts due, claiming you are due a credit, or that they have a new supplier for gas, all they need is your info - billing natually - to get things going. After the 3rd call, I called Washington Gas and confirmed that they have not called, and the numbers I gave them are not associated with any of their 3rd party contractors/suppliers.
So, Washington Gas is aware of them, but I guess haven't been able to shut them down yet.
Other numbers that I believe is part of this scam: