TORONTO - Complaints about banking services handled by an industry ombudsman surged by 28 per cent last year, with credit cards, mortgages and personal accounts drawing the most customer grievances.

The Ombudsman for Banking Services and Investments (OBSI) says it opened 370 banking-related investigations in 2017 to handle customer disputes for its clients, compared to 290 a year ago.

The dispute resolution firm says last year's surge in new cases marks the highest level the industry ombudsman has seen in the past five years.

The industry ombudsman handles banking-related complaints for Scotiabank, CIBC and Bank of Montreal, but TD Bank, Royal Bank and National Bank have opted to use third-party firm ADR Chambers Banking Ombuds Office. The third-party firm also handles investment-related complaints for all six banks and other financial institutions.

Customers complained most about credit cards, with the number of investigations last year nearly doubling to 112, or 30 per cent of all banking cases.

Mortgages were the second-most complained about product, prompting 67 new investigations last year, followed by personal accounts with 61.