This is a scam. After a few times of ignoring the call, I googled the number and saw it was apparently associated with Pepco, so the next time they called I answered. The woman said she was calling about the "disconnect notice". She gave me another number to call-800-341-8225
to resolve the billing problem. I called it and the man who answered said they were disconnecting our power in 45 minutes and to make an express payment I had to go to 7-11, buy a "Moneypak" card, and send $330.60. At that point, I realized it was a scam. Re-googling the number, it was clear it was an old Pepco number, no longer in use. So, lesson reaffirmed: do not answer calls from strange numbers where the person doesn't leave a message. And block them.