As many as 4,000 new PPI complaints are still being received every week by the financial ombudsman.
In its annual review of complaints for 2015-16, the Financial Ombudsman Service (FOS) said PPI (payment protection insurance) remains the most complained-about product, and it still receives up to 4,000 PPI cases each week.
The ombudsman said it received 188,712 new PPI cases in 2015-16 - making up just over half of its workload in the last financial year. Around one in five PPI cases are resolved within three months.
In total, the ombudsman, which resolves disputes between consumers and financial firms, received 340,899 new complaints in the last financial year.
Some 438,802 complaints were resolved in the last financial year and 51% of cases were upheld in the consumer's favour.
Meanwhile, complaints about "packaged" bank accounts more than doubled in 2015-16 compared with a year earlier, with 44,244 new packaged bank account complaints in the last financial year. In 2014-15, the ombudsman had received 21,348 new complaints about packaged bank accounts.
Packaged accounts tend to bundle up a range of perks, such as travel insurance, in return for a monthly fee. But the accounts have been controversial as some people have found the perks to be not what they expected or they have found they are not eligible for certain policies.
Rules surrounding packaged accounts were tightened in 2013, forcing financial institutions to check whether a customer is eligible to claim under each policy.
The ombudsman's figures also show complaints about payday loans nearly tripled in 2015-16, with 3,216 new complaints, compared with 1,157 in the previous financial year.
The ombudsman service said the growth in payday loan complaints reflects consumers' growing levels of awareness of their rights. The payday loans industry has undergone a huge clampdown by regulators in recent years to help prevent people taking on unaffordable debt.
Chief ombudsman, Caroline Wayman, said: "It's been another year of big numbers and big changes for everyone. But we mustn't lose sight of the lives and livelihoods behind every complaint we resolve.
"That's why preventing mistakes of the past from happening again will help restore trust and fairness in financial services."
The Public Accounts Committee (PAC) recently warned there are "serious risks" of further mis-selling scandals erupting in the financial services industry and said stronger action is needed to tackle problems with the culture of firms.
Packaged accounts were highlighted by the PAC an as a potential area for concern.
The PAC also said it is a "failure of the system of regulation and redress" that claims management firms have made up to £5 billion from PPI payouts. This is compensation that could - and should - have been paid to the victims of mis-selling, the PAC said.
Claims management firms typically take around a quarter or a third of compensation payouts - but people can make a complaint to a firm themselves - and to the ombudsman - for free.
Alex Neill, Which? director of policy and campaigns, said: "The huge number of PPI complaints still going to the ombudsman is yet more evidence that the systems the regulator and banks have put in place have not worked.
"Too many people have been driven to use claims management companies that are taking a large proportion of the compensation they are owed.
"Banks and other providers must make the process simpler and easier for customers to claim directly, or pick up the tab when consumers use claims management companies to get back the money they are owed."