Families are being left hundreds of pounds out of pocket due to errors by firms calculating their household bills, new research has found.
Customers were overcharged by a total of £6.7 billion last year by companies issuing essential bills, including utilities, telecoms and mortgage providers, according to a report by price comparison website uSwitch.
It found 70% of consumers were overcharged on at least one household bill in the last 12 months, with 95% of cases spotted by the customer rather than the bill provider.
A third (33%) of customers were overcharged more than once, while one in 10 had fallen victim more than three times in the last year, according to the survey of 1,000 people.
The average amount people were overcharged was £196, while one in 10 (11%) said they were overcharged by at least £400.
The most common causes included charges being added that should not have been (42%), incorrect tariff or product details being used (32%) or a special offer or discount not being applied to the bill (25%). A quarter of consumers (25%) said they had received a household bill that simply did not add up.
Ann Robinson, director of consumer policy at uSwitch.com, said: "Overcharging on household bills is rife and yet it still seems to be down to the customer to spot it.
"Consumers have to keep their wits about them and ensure that they check all their household bills carefully - if you are not checking then the chances are that a mistake will have slipped through and this could be costing you dear. At the same time I would urge companies to do as much as possible to help their customers by making household bills simpler, clearer and easier to understand."
The average time consumers had to wait for reimbursement was 53 days, the survey found. Some 13% of customers had to wait between two and six months, while 12% were still trying to get the issue resolved. About 6% of consumers said they never got their money back again.
The survey also found that on average people spent eight hours and £23 on phone calls and correspondence trying to sort out mistakes, with just 7% receiving an instant refund.