Westminster City Council has invested in providing free cold call blocking devices for vulnerable residents' landlines, after revealing one woman was receiving 147 nuisance calls a month.
She narrowly avoided being fleeced of £9,000 after nearly falling for a call from a scammer pretending to be from her bank's fraud team.
They claimed her account had been compromised and she needed to transfer money abroad immediately as part of an "undercover operation".
The caller even claimed they would arrest the suspect when they tried to withdraw her money, so she visited her bank and made the transfer, but became suspicious when she spotted anti-scam material at her branch.
She contacted her bank when she returned home, and police were able to recoup most of the money being transferred abroad.
The scam victim has since had a Truecall device installed for free by Westminster City Council, and said it had ended the hundreds of calls which often woke her at night.
"After I received the call from someone claiming to be from my bank I was very worried," she said. "I expected the worst every time the phone rang, but not anymore."
The case was detailed by the council, which has started a project with Truecall to install call-blocking devices on landlines for the borough's most vulnerable residents.
Truecall estimates installing its devices will save Westminster an estimated £31,140 in NHS and health and social care costs by blocking calls that could have taken a toll on people's financial and mental health; also saving an estimated £34,400 of vulnerable households' money from scams.
Truecall director Steve Smith said scammers and cold callers used so-called "sucker lists" made up of phone numbers of victims other callers had managed to scam or convince to buy over-priced products.
That was how some victims came to receive hundreds of calls a month. He said elderly and vulnerable people also wound up being persistently called as they may have sounded confused on the phone, and deemed worthy of follow-up attempts.
Mr Smith said some cold call sales pitches were not a scam, but exploited vulnerable people's confusion. He referenced vitamin pill sellers who phone elderly people to repeatedly sell overpriced supplements.
These often came to light when the person's carer found a cupboard stacked full of vitamins.
The Truecall devices use techniques to stop nuisance callers from getting through to residents' landlines from call-blocking a flagged number list, to stopping automated calls, blocking foreign numbers or even blocking all numbers on a not-approved list.
Mr Smith said his company worked with about 160 local authorities, police and charities to provide the call-blocking services to the elderly and vulnerable. He said Truecall had also been asking mobile phone network providers for some time to engage with them on extending the concept.
Westminster Trading Standards will be installing the devices for free for local residents and their families who contact them to complain of consistent nuisance cold calls.
Cabinet member for public protection and licensing Ian Adams said the small cost of the project would yield valuable results.
“Telephone scams are incredibly sophisticated, and would challenge most members of the public, and leave vulnerable residents defenceless.
"What’s worse is the fact that these are not indiscriminate attacks, but directed at vulnerable people.
"These nuisance call blockers can have life-changing results, and have given these victims of crime and their families peace of mind."