How can i get rid of a hard core salesperson whos trying to sell us their business?

in an energy company like con edison,they call us everyday sometimes three times a day,i hang up in their faces and threaten them but to no avail.they keep on pluggin.we have con edison ad i was told to just tell them that we are renting and cannot give a straight answer.i goy their phne number and will call them back and say thanks but no thanks.what balls they have calling us at all hours of the day.