Teams of officers working for National Trading Standards (NTS) identified 10,843 victims in the year to April.
The average loss was £1,184 - about £13m in total - but officers think hidden losses are much higher.
They identified nearly 200,000 potential victims on so-called "suckers lists" sold between con-artists.
Overall, NTS estimates that prize draw scams cost the UK public £60m a year, with an estimated 380,000 victims each year.
In one case, officers in Merthyr Tydfil visited a woman who was addicted to responding to scam mail. Her life savings had been spent and it took time for her to talk to her family about what had happened and to take control of her finances again.
Officers said that older, more vulnerable, people were being targeted.
Over the year, they secured more than £385,000 of compensation for victims, although this was still a fraction of total losses.
NTS oversees specialist teams tackling scams, illegal money lending, and online fraud. It published its first consumer harm report on Monday, building on data published earlier in the year.
It estimated that teams under its umbrella disrupted and prevented £252m worth of losses to consumers and businesses in a year, prevented more than 2.5 million unsafe or non-compliant goods from entering the supply chain, and convicted 100 criminals who are serving a total of 118 years of prison time.
Lord Toby Harris, who chairs the NTS, said: "It is not just money they take from innocent people. Many victims feel they have lost their dignity, their self-confidence, their sense of security. For small businesses, entire livelihoods may be lost and this, in turn, damages the economy.
"We have limited resources and I am all too aware that in many areas we may only be skimming the surface of the problem, particularly when it comes to the internet which is notoriously difficult to police."
Victims of scam mail have an average age of 74 and have typically lost more than £1,000, investigators have confirmed.