Legal discourse against builder in case builder is harassing residents

Dear Sir, I live in Greater Noida West where builder is exploiting residents in many ways, maintaining society from his sister concern facility company and not forming AOA/RWA from last 3+yrs. He also check and take personal post of residents even registered post since many residents complain to Govt authorities for same. It happens many times that registered post are either not delivering to residents or they are delivering with delay. when checking on POD of these post status shows that these posts are delivered 2-3 days before. residents have doubt that facility takes these post, open, read and then send to residents only if it does not have any post against builder. What all proofs we should have and what all legal action can be taken against builder and his facility company.