It's legal-ish. Some sales people will ask to see your bill. There is a number on there they can use to switch your account. At that point it's fraud if you don't agree to it - but from what I've heard it's hard to get anyone to really care about it. If you didn't show them your bill, there isn't much you can do now.

In the future, if someone is going door to door and they don't have a vendor badge you can contact OCP by phone at 410-313-6420 or by e-mail at consumer@howardcountymd.gov , or call the non-emergency police number.