Elderly people in Leicestershire are being warned after reports of residents being threatened by a company claiming to sell double glazing.
The county council said it had received 12 complaints about a company claiming to be called Bowater.
Trading standards said some people were threatened with fines, "green taxes" and even a death threat.
Officials want to know if anyone else has received any such calls and urged people to be on their guard.
David Bull, head of Leicestershire County Council's trading standards, said: "It is sickening that older people are being threatened with fictitious taxes or fines, the loss of benefits or even death.
"We are very concerned that this firm is deliberately targeting older people and we would urge people and their relatives to report all cases to us via Consumer Direct on 08454 04 05 06.
"Reputable companies do not pressurise or threaten people."
The council said in cases reported so far, callers phoned older people and told them they qualified for a government grant to have their windows replaced.
When the resident said they were not interested, they were told their phone call was being recorded and they would be reported to their district council.
The caller then threatened the resident with a fictitious "green tax" and the cancellation of their single occupancy council tax reduction.
In one case, a resident was threatened with a £1,000 fine if they did not complete a survey of older people in the area.
On another occasion, the caller said the resident would be killed.
Paul Shipman, 68, from Broughton Astley, said: "The salesman started out saying that there were new British standards and I needed new windows but when I showed no interest, he threatened me with a green tax.
"When that didn't work, he threatened to put my head in a vice and watch me bleed to death.
"He was very threatening - in the end, he said he'd come round and kill me."
The Glass and Glazing Federation said it was not aware of any current company called Bowater, adding there was a firm with that name several years ago, but they were taken over and had not used the name since.