Occupation certificate promise on sale agreement broken

I have purchased an Bruhat Bengaluru Mahanagara Palike (BBMP) approved apartment (with almost no deviation from BBMP approved plan) in Varthur area of Bangalore. The builder has still not provided the occupation certificate (OC) which it promised on initial sale agreement (registration is already done after this, so not sure whether that sale agreement is still valid or not). He always asks pending amount from 'some flat owners' who have not paid some amount because the builder has not completed work for them until today. I would like to get help on following things, thanks in advance ! 1. In absence of apartment association, can individual buyers have any online way to file a court case / serve a notice to builder to get the OC document asap. (I heard of e court but not sure whether this would be helpful in this matter or not) 2. If court case is not possible online (flat owners don't want to indulge with never ending battles in courts), will a notice from a lawyer have any legal value/boundation on builder to get this work done? 3. What are the other possible ways flat owners can initiate to get this done?