Executives of three of the nation's largest health insurers told federal lawmakers in Washington that they would continue canceling medical coverage for some sick policyholders, despite withering criticism from Republican and Democratic members of Congress who decried the practice as unfair and abusive. An investigation by the House Subcommittee on Oversight and Investigations showed that health insurers WellPoint Inc., UnitedHealth Group and Assurant Inc. canceled the coverage of more than 20,000 people, allowing the companies to avoid paying more than $300 million in medical claims over a five-year period.