Demand letter sent without CC/OC and unfit flat not yet complete

Builder delayed by 3 years now flat not ready for living yet asking for final demand for possession not furnished OC/CC No inspection of flats no testing of water, sewerage done Very poor quality of cementing of walls and fittings like aluminium window frames , wooden door looks 10 years flat Electrical piping done without junction box and earthing missing etc several negligence No car park allotted No sanctioned plan and layout shown or sent No amenities complete yet Some built some no space to built Asking for increase sqft without relevant docs Asking for more tax due to GST How will measurement take place carpet and balcony area separate, how to determine proportionate open area/common area in super built How to treat roof and car parking space, Builder has roof right ( measurement) Denying late penalty even after giving in letterhead that he will pay bank interest after said date Coming up with excuse for delay as 7th floor sanction got delayed from authorities which was never informed to us How to reply on demand letter and ask for habitable possession which is with all legal docs How to sue him under contracts law for fraud and risking people life How to appeal under Consumer protection law There are more than 100 people