About one in seven people could be paying a “loyalty penalty” for products such as mortgages and mobile and broadband packages, according to Citizens Advice.
The charity said some UK households could save as much as £400 by switching, or seeking discounts, from their current suppliers.
Citizens Advice also said analysis of the budgets of 165,000 people who came to it for help with debts suggested people on lower incomes can end up spending nearly double the proportion of their income on telecoms that those earning more do.
Citizens Advice said it heard from a woman called Tracy who signed up to a £30-a-month package which included TV, landline, broadband and international calls in 2006. She relies on disability benefits.
In January this year, she started working through her bills to look for potential savings and was shocked to see her bill had increased to £80 a month over the years, the charity said. She has now switched providers.
She told the charity: “Everything is going up: gas, electric, food, and I have a mortgage to pay. I shop late in the evenings to get yellow-sticker discounted food, I turned off my gas as I can’t afford to repair the boiler or use the heating and I don’t go anywhere other than my hospital appointments.
“When I asked my broadband provider why I wasn’t told about the increases, they said I should have checked my payments and contacted them to see if there was a cheaper deal.”
The charity submitted a “super-complaint” about loyalty penalties in the mobile, broadband, home insurance, mortgages and savings markets in 2018.
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Measures to protect home and car insurance customers from loyalty penalties were introduced by the Financial Conduct Authority (FCA) in January this year. The changes mean insurers are required to offer renewing customers a price that is no higher than they would pay as a new customer.
Mike Emmett, who runs training for advisers at Citizens Advice Cardiff and Vale, said: “Many people see their mobile and broadband as a lifeline. They need them to speak to people and do things like manage their universal credit account, and help their kids with their homework.
“But they’re usually reluctant to switch for fear of rocking the boat, particularly because of the prospect of credit checks. We also find people who are digitally excluded or who have mental health problems often prefer to speak to someone about switching, but they can wait for hours on the phone and end up giving up.
“It’s so frustrating when we see people who are on the lowest incomes paying the loyalty penalty, as they’re forced to jump through so many hoops to try to sort it.”