Top health insurance companies told members of Congress Wednesday that more than 80 percent of people who've signed up under the president's new health care law have gone on to pay their premiums — a necessary step for the enrollment figures touted by the Obama administration to hold up. Aetna reported payment rates in ''the low- to mid-80 percent range;'' Wellpoint said the rate was as high as 90 percent for those whose premium had come due; and the Health Care Service Corporation, which sells Blue Cross Blue Shield plans in five states, pegged the rate at 83 percent or above.