Time frame for compensation for delayed posseion of property

We booked a flat and registered in Nov 12. As per the the agreement, possession was on June 14, with grace period of 6 months. We have paid 85% of flat cost till now and now received demand note for balance payment with common maintenance charges etc. Developer has not provided any amenities as shown the plan like swimming pool, club house etc. We are following up with builder for past 6 months for compensation and completion of project with amenities. But developer has sent separate letter with demand note stating reason for delay and keeping the right to escalate the price. Probably just to counteract our claim in advance. My question is : 1. Shall we pay balance payment, take possession and then file a case of breach of contract? Whether such a case stand in consumer court? 2. As per our agreement, developer will pay 12% pa for the delayed possession in case we cancel the agreement. During verbal discussion, developer has shown inability to pay any money as compensation. Is it advisable to cancel the agreement, file the case to get compensation as this clause? 3. Can we deny to pay common maintenance charge (not listed in agreement) and still take possession legally.