Hi
1) First issue legal notices to your builder for deficiency of service
2) If there is no commitment of favorable response, file a case in the consumer court.
3) You can issue legal notices and file court cases either individually or collectively depending on your convenience.
4) The builder has no right to stop a formation of association. If there are around 8 willing flat owners, you can form an association and register the same with registrar of societies. then the builder will need to come to you only.
5) BBMP will not be of help. Their only help could be in prevailing upon the builder to complete the building as per sanctioned plan and amenities and then issue the Occupancy certificate.
6) It is the builder's job to get the Occupancy certificate and he should do it at his own cost. Flat owner's need not pay for occupancy certificate.
7) Please be informed that consumer courts are very aggressive in the recent past and have been issuing orders favorable to Flat owners
For your information, from internet you can find out how flat owners (Through consumer courts) have literally won cases against leading builders like Amrapalli(Dhoni was a brand ambassador for this company), Unitech, Jaypee, HDIL, Emar MGF, Parsvanath, Shobha etc and have been able to get a fair compensation for the sufferings the flat owners had undergone .
All it takes is for one flat owner to approach the Consumer Court to bring builders like Prathap Reddy to their knees.
Hope this helps.