Millions of consumers have been plagued by incorrect bills.
An annual survey has highlighted the worst firms for billing customers poorly.
The body ranked in at the top spot for the worst offenders after revealing that almost six million people had paid the wrong amount of income tax through the Pay As You Earn system due to an internal error – some customers were given a rebate for paying too much where as others were informed that they would have to pay back what they owed in instalments.
Energy companies came second in the list after 27% of households complained that they had received incorrect bills. This has resulted in over 10 million households owing between £200 to £400 to their energy provider.
Other organisations in the top ten included council tax departments, water companies and credit card providers.
Ann Robinson, director of consumer policy at uSwitch.com, said: “Inaccurate bills are no laughing matter for consumers, who can end up out of pocket and wasting time and effort trying to resolve billing blunders”.
She added: “The fact is that households are at the blunt end of hugely varying standards in billing accuracy, with some industries, companies and organisations performing noticeably better than others and some consistently coming in at the bottom of the class”.