This is national grid. It is the same number that called me in the past when my bill was overdue. That wasn't a scam; my bill really was overdue. But I still didn't pay it by phone, I simply paid it electronically the way I pay all my bills, once I had the money to do so.
Currently, they are calling to schedule replacing my meter free of charge. This is because Mass state law requires the replacement every 7 years, even if the meter is fully functional. I converted from oil to gas seven years ago. Scam? No, not in my case.
But I'm glad so many others are suspicious in general. That is a healthy skepticism. For me, it checks out in this case.
several repeat calls from this number within an hour. It is Natl Grid collections. They even call when an account has been paid in full. Possibly to verify your phone number.
I also got a call from this number. National Grid confirming an appointment I did not make. I am a National Grid customer but they do not have my cellphone number on my account.