Can I cancel marriage after engagement

Sir, I got engaged to a girl, then we started chatting first casually. Then on one sudden day after 20days of chat I got to know she has thyroid from 12 years which was kept hidden from us. We did sexting but no pics no videos nothing, just text chats sexually that too with mutual consent. Once we got to know above issue we don't want to proceed further, and once my parents agreed I stopped chatting to her, so we dropped off same has been told to them. Now they are asking money around 10Lac. Or do marry the girl. Being a middle class member affording that much money is nowhere possible for me. They have every recordings of our calls we did to them. Even they called my mom and talked improperly and rudely, which is again not recorded. (Any chance to get recordings of the call)..? The mistake I did here is I deleted my chats because I felt keeping out of our chats in public may girl can feel insecure, but they are utilizing my week points and asking money for collecting pics of a girl w.r.t engagement and etc. My entire family is tensed/scared from the day when we told them we don't want to marry. I am confused what to do.