Nov 19 (Reuters) - Australia"s corporate regulator said on Friday it was suing MLC Life Insurance for causing financial harm of A$17.5 million ($12.73 million) to over a quarter million customers by not paying benefits and charging premiums without notice. MLC is a part of Nippon Life Insurance (NPNLI.UL), Japan"s biggest insurer. It was formerly owned by National Australia Bank (NAB.AX), which now retains a 20% stake in the firm. The Australian Securities and Investments Commission (ASIC) has accused MLC of service failures resulting from poor systems and controls over a period from 1999 to 2020, which caused financial harm to over 260,000 customers. The allegations include denying insurance cover to customers suffering from severe rheumatoid arthritis and failing to pay benefits to customers who were undergoing rehabilitation after an insured injury or disability. "Consumers should be able to trust insurers to pay their full benefit in times of need and keep them informed about significant changes to their policies, " ASIC Deputy Chair Sarah Court said in a statement. MLC has already remediated customers impacted by the alleged conduct, the ASIC said. However, the regulator said it was seeking enforcement action to improve the systems within the insurance industry that enable consumers being harmed by implementation issues. MLC did not immediately respond to a Reuters request for comment. ($1 = 1.3742 Australian dollars)