i presume cooperative society has been formed for your building . there is a procedure prescribed for redevelopment in maharashtra .
from facts mentioned by you it appears that your society has not appointed any consultant , floated any tenders before going in for redevelopment . further video recording of proceedings have to be done .70%of members have to agree then only redevelopment can be done after resolution is passed in AGM and redevelopment agreement signed by builder with society and flat owners .
if builder has committed breach of terms of agreement society can terminate the agreement with builder and encash the bank guarantee . contact a local lawyer