Builder delaying amenity work after handover

Hi i have purchased a flat in Navi Mumbai and 2 years back got possession of that. But builder has not yet completed on agreed basic amenities like Gym, Society gates, security, internal lighting, cctv etc... All flat owners has jointly given him 3 notices regarding all pending work. But he is delaying all work giving reason of due to covid finance and worker shortage is there. However his other new project within 2 km from our society he has almost finished all work there in same duration. We are aware that he is purposely delaying all work. Now he has sent letter to pay all next year maintenance as well. Last year we have paid him complete year maintenance as it was mandatory to get the possession. Now since half the amenity work is not yet ready what option we have? Questions actually here: 1. What action we can take against builder as he is delaying amenities work. 2. Without delivering amenities he is asking for complete annual maintenance and mentioning penalty amount for delay of payment. Is our stand of no payment to him till all work is complete is valid? 3) What to do if builder is delaying the society formation and handover. Kindly advise.