This is Smart One Energy. They use caller ID spoofing, which means that the number that shows up on your caller ID is not the number they are calling from. Some of their sales people also say (fraudulently) that they are calling from Washington Gas and that you qualify for a discount on your bill, and that they want to verify your account number. DO NOT give them your account number unless you want to switch gas suppliers. They will take it and switch you from Washington Gas to their company, without your permission.
How did they get your phone number? Washington Gas provides third party companies with your home phone number as part of the new competitive supplier market. You can opt out for one year by calling Washington Gas between 9/1 and 10/13 and asking to enroll in "Opt Out" so that your home phone number will not be shared. You will have to do this every year, however.
Contact the Maryland Public Services Commission at 1-800-492-0474
Tell them
1. Smart One is calling you repeatedly
2. Smart One has not respected your request to be removed from its list
3. Smart One is using Caller ID spoofing to prevent call blocking and screening
4. Smart One is misrepresenting itself as calling from Washington Gas
5. Smart One is claiming that it is Washington Gas and wishes to verify your account number in order to trick you into giving them your account number