Payday lending giant CashEuroNet, which owns Quick Quid and Pounds To Pocket, is the most complained-about banking and credit business.
Complaints against the payday lender trebled to 4,692 in the first six months of the year, said the Financial Ombudsman Service.
The high-cost credit company knocked Barclays Bank off the top of the table, with collapsed lender Wonga third.
More than two-thirds of complaints were upheld against the payday lenders.
Some 72% of complaints were upheld against Wonga and 69% against Quick Quid. By comparison, only 28% of complaints against Barclays were upheld in the period January to July 2018.
Poor complaints handling
“These are astonishingly high uphold rates – higher than any other type of product the Ombudsman covers,” said debt commentator Sara Williams, who blogs as the Debt Camel.
The latest complaints data from the Financial Ombudsman revealed that complaints against payday lenders Sunny and Lending Stream were also upheld at high levels, 65% and 62% respectively.
A year ago, the Financial Conduct Authority wrote to all banking and consumer credit firms, demanding that they improve the way they deal with complaints.
“The current high levels of customer complaints being won at the Ombudsman suggests that the payday lenders have not improved their complaints’ handling enough,” said Ms Williams.
“Lenders are continuing to reject or make poor offers to customers’ complaints, even when they know from experience that similar cases are being routinely upheld by the Ombudsman. This is not treating their customers fairly.”
Britain’s biggest payday lender, Wonga fell into administration last month after a surge in compensation claims against the firm.