They were call me frequently as well asking to speak to the person that handles our natural gas account.  I explained that we are in a high rise office bldg and we do not pay for the gas utilities.....But they call and call and call....
I asked them to removed us from their list.  They said "Ok, we will do that."
But they continued to call and call and call.
One time I saw it was them calling and I answered the phone by saying, "NO!"
And the lady said, "Excuse me?"
I said, "Do you understand what NO means?"  She said, "Yes I do."
I hung up on her.
Guess what?
They called again the next day.
When I answered the phone I said, "Velvet's phone sex service.  How may I direct your call, baby?"
They hung up.
The next day they called back.  "Bob's propane heating, how may I help you?"
"I'd like to speak to the person that handles your natural gas account."
"Serious lady?  I just said 'Bob's propane' we only use propane."
She hung up.

Our phone service is through Nextiva and I figured out how to forward a phone number to a number of my choice.  So now I have that number forwarded right back to themselves at (313) 444-2924.
Good luck people!