Delays, overpayments, errors and entitlement disputes topped the list of complaints investigated by The Pension Advisory Service's (TPAS) over the past year.
The advisory service's annual review - published today - revealed TPAS had three million visits to its website, received more than 60,000 calls and 18,000 written queries in the year to the end of March 2013.
Over the year TPAS received about 4,500 complaints, more than half of which were not investigated.
Of the complaints it received, 46% related to defined contribution (DC) schemes, 29% were about a public sector scheme and 25% were about a defined benefit (DB) pensions.
A delay in paying benefits was the most common reason why someone complained about a DC scheme - with a third of such complaints being about delays. Some 30% of complaints about DC schemes were about a mistake or an overpayment.
A complaint about a decision was the main reason why people complained about a public sector scheme - with these accounting for 30% of all complaints against this type of scheme. Some 80% of these related to ill-health retirement applications.
The next most common reason was again due to a mistake or an overpayment - accounting for 28% of public sector complaints.
For DB schemes, 35% of complaints were because of a dispute over a member's entitlement. Mistakes and overpayments were the next most common cause of complaints from DB members.
The most common at-retirement complaint was due to a delay in a pension being paid.
Although the organisation said the number of calls related to pension liberation was relatively small, calls soared from 8 in April 2012 to 92 in March 2013.
In partnership with The Pensions Regulator (TPR), Action Fraud and other government agencies, TPAS launched a pension liberation fraud campaign in February this year.
Since then, there have been more than 20,400 downloads of leaflets for pension scheme members from its website.
Chief executive Marta Philips, who is due to leave the organisation shortly, said: "During my time as chief executive at TPAS I have been extremely impressed with the level of commitment and dedication our volunteers have shown.
"Although I am stepping down from my role at TPAS this summer, I am confident that such a vital service will continue to help even more people in the future."
In the last year, the service helped more than 80,000 people with their pension issues and recovered £7m worth of additional pension payments and compensation.
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