What should I do in a situation like this?

turn your phone on.call her for one last time and then don't call her at all or may be you should go to her house and try to talk to her or ask her friends about her and if she is ignoring then let her go and move on there are plenty of girls like hers.have a good life don't let a girl ruin your whole life and next time let the girl be a part of your life not your whole life. and grow up