Want to know how could I take legal step against my former female partner who has been black mailing

Sir/Madam, I have been with this girl from my early days of Post graduation and she had been both my professional and personal partner for almost 2 years. In recent past about last 9-10 months the girl has been blacking me, threatening me to label me, already has been defaming me, took all my financial and academic materials and resouces, also breached the consent of ethics even by taking the topic of research work topic that was jointly agreed, used and exploited me day and night by mental, physical and financial means to write academic papers for her, now her threatening of legal cases on false cases have reached almost a period of 10 months yet she has contacted me on her benefits, I have been physically manhandled many times by her and once by her male friend. She has my certificates and books in her possession also ursuped enough case lately. Again recently she contacted but after few days she is again blacking me and now pushing me to extend of mental creulty. I am helpless and I know being a male I am clueless as for a long part we both were romantically involved. What steps could I take?