About 1.8 million Australian mortgage holders are being urged to check their offset accounts. A new report by the Australian Securities and Investments Commission found lenders had to repay $55m to thousands of customers in compensation due to offset accounts not being used properly. Canstar data insights director Sally Tindall said offset accounts were a powerful tool but only if they are used properly. The report follows RBA data that shows 55 per cent of mortgages or 1.8 million Australians have an offset account, with $349bn stashed in them collectively. "When offset accounts don't operate correctly, the harm can be hidden.