How to legally get married if parents are opposing

Hi my parents have trapped me in my house because I wanted to marry my boyfriend they liked him and our families met and decided for our marriage as well we both are Hindus bt when they came to knew that we are not of same caste they refused I was working in different city where my BFF belongs not they have brought me to my hometown and are not letting me work in any other city as well . My boyfriends family is ready and we have decided to get married legally how can I get out of here and what actions can I take