WASHINGTON — The 60 million people on Social Security will not receive any cost-of-living increase in their benefits in 2016, the government said on Thursday, but because of a quirk in federal law, nearly one-third of Medicare beneficiaries could see record increases in their premiums unless Congress intervenes. With millions of older Americans on fixed incomes facing that one-two punch, the Obama administration is urging Congress to moderate or stop the health insurance premium increases, which could raise the cost for some Medicare beneficiaries by about 50 percent — the largest increase, by far, in the history of Medicare. But...