A "striking" surge in consumer complaints about credit, including payday loans, has been seen by the Financial Ombudsman Service (FOS) over the last year.
In its annual review of complaints, the FOS said complaints about payday loans tripled in 2016/17 compared with the previous year.
Some 10,529 complaints about payday loans were received by the service in 2016/17, compared with 3,216 in 2015/16.
More than half (59%) of payday loan complaints were upheld by the ombudsman service in consumers' favour in 2016/17.
Overall, there were 25,984 complaints about consumer credit products and services in 2016/17, compared with 13,713 the previous year.
Within the total, complaints about hire purchase were also up year-on-year,with 5,029 complaints in 2016/17 compared with 3,072 the previous year.
Complaints about catalogue shopping, debt collecting, hiring leasing and renting, point-of-sale loans, credit reference agencies, guarantor loans, and logbook loans - where the borrower's vehicle is put up as security - also increased year-on-year.
A huge clampdown on payday lenders has taken place in recent years, with firms now having limits on the amount of times they can roll a loan over and the amount of interest they can charge, to stop borrowers sinking into a debt spiral.
The Financial Conduct Authority (FCA) recently announced plans to put the high-cost credit sector under the spotlight.
Debt help charities have been raising concerns over Bank of England figures showing strong annual growth in consumer credit.
Charities have warned that borrowers could be at risk of over-stretching themselves, at a time when living costs have seen some strong rises and wage growth remains stagnant.
The FOS said it took on 321,283 new complaints in total in 2016/17, of which 53% amounting to 168,769, were about payment protection insurance (PPI).
Caroline Wayman, chief executive and chief ombudsman of the FOS said: "Whilst payment protection insurance (PPI) continues to make up a large proportion of the complaints we see, the most striking story this year has been the rise in complaints we've seen from people having trouble with credit. For example, we've seen around three times last year's volumes of complaints about payday loans.
"It's clear that financial difficulties and financial exclusion remain significant challenges for many people.
"The important thing is to speak up if you're struggling.
"Money is often very complicated, and our job is to unravel what's happened and find a fair way to put things right by looking at individual complaints."