Three Illinois residents who agreed to pay 139 percent interest on $2,525 in loans from Western Sky Financial — a “payday loan” company chartered in South Dakota that advertises on television and operates on the Internet — filed a state-court class action in Chicago against its owner, eight affiliated firms and some debt collectors, alleging that the defendants violated the Illinois Interest Act and the “unfair practices” provision of the Illinois Consumer Fraud Act.Western Sky and its …