There were 263 new cases involving Prudential, while Phoenix Life was second with 248 and Aviva was third with 222.
Sun Life (178), Friends Life (172), and Legal and General (155) made up the rest of the top six.
See table below for more.
The FOS also revealed data on cases it has resolved in the first half of this year, showing which companies had been ruled against the most.
Sun Life was top in the life and pensions and decumulation category, with 41% of cases resolved in favour of the consumer. Santander was tied in second with Countrywide Assured and Sesame – all at 36%.
Bank of Scotland was fourth at 31%, head of Reassure at 25% and Friends Life at 24%.
See table below for more.
Overall, the Financial Ombudsman Service took on 173,994 new cases in the first half of 2015 – an overall increase of 8% on the previous period.
The total figure was a rise from 161,649, with payment protection insurance (PPI) making up 55% of the complaints.
The average uphold rate (where the ombudsman found in the consumer’s favour) over the six month period was 57% – ranging from 5% to 94% across the individual businesses.
Twenty two financial businesses feature in the complaints data for the first time, meaning that 222 in total had 30 or more cases referred to, and resolved by, the ombudsman service in this period.