Please do call someone, this is neglect and is a crime in many parts of the world. Investigate what national help centers/phone lines are available or even better, local ones. Please don't let your own inaction be the reason that you or your sister have something worse happen. The work you may have to do in an environment that actually wants to take care of you and your sister but is foreign to you, is a much better option than the familiar yet indifferent one you are currently in. I wish you the best, and hope everything works out for you.