Blue Shield of California owes $24.5 million in rebates to thousands of small-business customers, and rival Anthem Blue Cross will return $12 million to small firms under requirements of the federal healthcare law. The annual rebates were disclosed in reports to state regulators, and the final tally from some companies may change before they are paid out by Aug. 1. The rebate is required under the federal Affordable Care Act when insurers fail to spend a minimum of 80% of premiums on medical care for individual and small-business customers.