"Mr. Robertson/Robinson" left message regarding the "supply portion of [my] electric bill. Please be sure to call back with your electric bill and reference number" blah, blah, blah.
So, yeah, he's not going to be getting a return call.
I had the same message as all the above posts and what they are fishing for is your account number for your electric company. Once they have your account number they will switch you to another electric provider without your consent. This is fraud.