CONSUMER complaints to the Financial Ombudsman Service (FOS) have soared more than fifty-fold over the past decade to reach a total of 265,000 new cases in 2011/12.

Experts do not expect any let-up in the current year, with forecasts of a 40% leap to 375,000.

The high numbers are a serious indictment on our banks, credit card firms, insurers, pension and investment companies. The deluge also threatens to overwhelm the FOS, which has outlined plans to recruit 1000 extra staff to deal with the flood of inquiries.

Tony Boorman, deputy chief ombudsman, says: "While we see some businesses using complaints positively to improve customer service, many continue to frustrate their customers with delays and inconvenience."

Many companies are simply flouting the rules. For example, cases are often referred to the FOS because a firm has not issued a final decision to the consumer within the eight weeks allowed under guidelines set down by the Financial Services Authority (FSA).

Complaints about the mis-selling of Payment Protection Insurance (PPI) make up the bulk of the FOS workload, accounting for 158,000 of the total 265,000 new cases. But there has also been an increase in the number of non-PPI cases: 107,000 in 2011/12, compared with 102,000 the previous year. The FOS expects the number to rise to 125,000 next year.

Payday loans and packaged accounts are two areas of particular concern. The FOS received 296 complaints about payday loans in the whole of last year compared with 271 in the first half of 2012/13. Its casebook suggests many payday firms are lending money to people who cannot afford the repayments. There is also evidence they do not always act fairly when they try to recover any money due.

Packaged accounts are simply current accounts with added extras, such as travel insurance and breakdown cover. They also come with a monthly fee, which could be as high as £25. Clydesdale Bank currently charges £12.50 a month for its Signature packaged account, but the fee is due to rise to £13.50 on April 1 – the second rise since it was launched with a fee of £10.

Packaged accounts have become increasingly prevalent in recent years as banks have sought to boost their profits: about one-third of current account customers now have a packaged account, often as a result of a hard sell by counter staff.

But there is growing concern that many people have unwittingly signed up to a package account they neither wanted nor needed. Some customers were also found to be ineligible for one or more of the insurance policies included.

The FSA has already announced a crackdown on packaged accounts and will introduce new rules in March to force banks and building societies to check a customer's eligibility for any insurance policy included. They will also have to issue an annual statement detailing the benefits of the account.

Sylvia Waycot of Moneyfacts says: "Sadly, the majority of packaged accounts offer a bundle of insurances such as break down cover, which can turn out to be worthless."

If you have a complaint about a financial product, you should in the first instance contact the relevant company. If the firm is registered with the FSA, it should have a complaints procedure in place, with a set time frame.

It's best to complain in writing, so that you have a record of your correspondence. The company then has eight weeks to respond, either resolving the issue, or explaining the need for more time.

If the company does not respond within eight weeks, or you are unhappy with its decision, you can contact the FOS. The FOS is a free independent service and about 50% of complaints are upheld in favour of the customer.

If you are still not satisfied, you could consider taking legal action, though it could prove costly and time-consuming.

Many organisations, including the FOS and Which?, can help with the complaints procedure, in some cases supplying template letters for ease.

You might also be contacted by one of the many claims management companies that have been set up in recent years. If the company is legitimate, it can save time and hassle because it will pursue the claim on your behalf. But the service is not free. Most operate on a no win, no fee basis and typically charge 25% plus VAT of any refund. If your claim is pretty straightforward, it is a high price to pay.