Complaints about "payday loan middlemen" websites that take hundreds of pounds from consumers on the promise of finding cheap credit have more than doubled in the last year, the ombudsman has said.
This year so far, more than 10,000 people have contacted the ombudsman to complain about credit broking websites, which is over twice the number for the whole of 2013, the Financial Ombudsman Service (FOS) said.
The service found that many people who had turned to such websites felt "misled" as they thought they were applying for a loan directly and did not realise that they were paying a middleman.
It said consumers who have contacted it were struggling financially and complained of payday loan middlemen draining money from their accounts, without providing them with the loan they were looking for.
Common themes in consumer complaints have included consumers not recognising the business that took the fee and saying they did not give permission for the fee to be taken.
In some of the worst cases the ombudsman has seen, consumers' bank accounts were debited multiple times without warning, as their banking details were passed onto other credit broking websites.
In one case the service said it has seen, a woman was charged on around 20 occasions for fees and up to £70 was taken from her account each time.
The service said that in two-thirds of complaints it investigated, the ombudsman agreed that the consumer had been treated unfairly.
In the majority of cases, the business running the websites refunded the cash they had taken as soon as the ombudsman got involved and in some cases people received refunds within 24 hours.
Senior ombudsman Juliana Francis said: "It's disappointing that people who are already struggling to make ends meet are being misled into thinking that these websites will get them a loan.
"In too many of the cases we sort out, no loan is provided and people's bank accounts have been charged a high fee, often multiple times.
"If money has been taken from your account unfairly or without warning, the good news is the ombudsman is here to help. Give us a call and we can put things right quickly."
Russell Hamblin-Boone, chief executive of the Consumer Finance Association (CFA), which represents short-term lenders such as The Money Shop, Quick Quid, Cash Converters, Payday UK, Peachy and Sunny, but does not represent credit brokers , said: "The problems caused by some brokers and lead generators bring the whole market into disrepute not least because it is hard for most customers to tell the difference between lenders and these middlemen."
He said the CFA agrees that middlemen companies should be clear that they are not lenders.
Mr Hamblin-Boone said anyone looking to arrange a loan should take time to check that the business is properly authorised to operate.
He continued: "Most importantly, if you aren't certain about the business or their service, never disclose your personal and bank details."
StepChange Debt Charity head of policy Peter Tutton said: "We continue to see numerous cases where financially vulnerable people suffer at the hands of brokers who take money from their accounts but fail to deliver on the promise of a loan.
"This is a well-known problem, but it continues to get worse. The time has come for government and the regulator to ban credit brokers from charging up-front fees."