The telecoms regulator is capping the cost of calling the 118 directory enquiry service to £3.65 per 90 seconds amid concerns about steep price rises.
Ofcom is imposing the maximum price from April 1 after some providers were found to be charging almost £20 for an average 90-second call.
Director of consumer policy Jane Rumble said: “Directory enquiry prices have risen in recent years, and callers are paying much more than they expect. Our evidence shows this is hurting people, with some struggling to pay their bills.
“We’re taking action to protect callers by capping 118 prices. This will significantly cut the cost of many calls, and bring them back to 2012 levels.”
Market leader 118 118 charged £11.23 for a 90-second call and people tend to call the numbers they most easily remember even when there are cheaper service available, Ofcom said.
It estimates around 450,000 consumers a year are paying £2.4 million in total more than they expect for these calls and some are struggling to pay their bills.
More than a million people in the UK – many of them elderly – still use the services, according to Ofcom research.
The number of calls being made to 118 services has been falling by around 40% a year.
People aged 65 and over, who are significantly less likely to have internet access, are four times more likely to call 118 numbers than 16 to 34-year-olds.
Ofcom’s research found that 65% of 118 callers did not know how much calls cost and 42% said they had no alternative to a directory enquiry service at that time.
The regulator said the price cap will protect callers from the shock of high bills and make directory enquiry services more affordable.
The 8% of directory enquiry callers with affordability issues said they cut back on spending on other items or borrowed money from friends or family to try to cover the costs. Some also delayed payment or defaulted on their bill.
Ofcom said there are nine directory enquiry services that have a 118 number, with published service charges of £15.98 for the first minute of the call and £7.99 for each subsequent minute.
The 118 numbers were introduced by Oftel, the previous telecoms regulator, in 2003.
The directory enquiry market was opened up to competition and a wide range of competing 118 services were launched.
Ofcom said the April introduction should give providers time to adjust prices and billing systems.
Minister for digital Margot James said: “It’s about time that this horrendous ripping off of customers was brought to an end.
“The new price cap will go a long way in protecting consumers from astronomical fees, and is part of a series of measures we have worked with Ofcom on to secure a better deal for consumers.”