In its annual review for 2013/14 the said it answered 2.3m enquiries from consumers and settled a record 518,778 disputes – more than double the number last year.
Payment protection insurance (PPI) made up 78% of all cases, with the number of PPI complaints rising 6% to 399,939.
Chief ombudsman Tony Boorman (pictured) said: “It’s been an unprecedented twelve months for the ombudsman by anyone’s standards. Complaints continued at record levels – and we resolved over half a million cases during the year.
“But our work – and complaints handling in general – is about much more than closing cases and reporting big numbers.”
He added: “Each case we see tells a story about the lives and livelihoods of the individuals involved. In our experience, people are simply looking for honest, straightforward answers that show someone has listened and helped make sense of things.
“So whether it’s dealing with a complex pension complaint or problems with a mobile banking app, the financial services sector continues to face the challenge of putting the customer at the centre of their business.”
FOS said in 58% of the cases we resolved we found in the consumer’s favour.
Almost a quarter of the enquiries we received were about general financial problems and concerns – and weren’t product-specific. And about one in five initial enquiries turned into a formal dispute – a record 512,167 new complaints.
Four of the UK’s largest banking groups accounted for 63% of all complaints we received. Other than PPI, it resolved seven out of ten (71%) complaints within six months.
It was revealed on Sunday that SIPP complaints were up 50% in the past year.