Women in the global south often seek justice of online harassment through unavailing the harassers and the screenshots of their sent harassment texts and visual contents on social media. However, women often experience further backlash with the argument that these screenshots may have been manipulated. We studied these issues through a survey with 91 female Facebook users and interviews with 43 females and other stakeholders from Bangladesh and designed 'Unmochon'-a tool that helps women collect such harassment texts and visual contents from Facebook Messenger, share with their intended group of users and prove their authenticity. Our user-study with 48 participants revealed various challenging aspects of seeking justice on social media using such technologies and the assumptions they are built on. Based these findings, we further discuss how technologies should be designed to address women's harassment on social media in such a complex social setting.