Sesame remained top of the list, with 172 complaints, 27% of which were upheld.
Openwork was second (111 complaints), Interactive Investor Trading was third (75) and Hargreaves Lansdown was fourth with 60 complaints.
Positive Solutions was in the top five for the first time, with 51 complaints and a 39% uphold rate.
Lloyds, Barclays, HSBC and RBS all topped the list for the highest number of new cases received, while Prudential came top for the most amount of life & pensions complaints.
Overall, the ombudsman took on a total of 173,994 new cases in the first half of 2015 – an overall increase of 8% on the previous period (161,649).
Of the total cases referred to the ombudsman in the first half of 2015, PPI made up over half (55%) – with 94,091 new PPI complaints, a 10% fall compared with the previous period.
For complaints about financial products other than PPI, the number increased to 79,550, a rise of 45%. This largely resulted from the increase in complaints about packaged bank accounts brought by claims-management companies during this period.
Chief ombudsman Caroline Wayman said:
"It’s been seven years since the ombudsman first began to publish data about individual financial businesses.
"This has coincided with a period of volatility and challenge for much of the financial services sector – and this is still reflected in the data we publish today.
"Complaints about PPI continue to make up over half of our workload. And though the number of new PPI cases has reduced in the first half of this year, the decline has not been as steady or as marked as generally expected. This is at least in part due to the continued high levels of activity by claims managers in this area.
"Claims managers have also been largely responsible for the substantial increase in complaints about packaged bank accounts, which have driven up our banking workload over this period by two thirds.
"Nobody wants “another PPI ”. This is why we’re working closely with businesses, claims companies and their regulators, to make sure PPI is sorted as fairly and as quickly as possible for everyone involved – and that lessons are learned to prevent anything like this happening again. If we can all achieve this, then the next seven years should be a different story."
