Legal remedy against CIDCO's letter for vacating

We have a property in Navi Mumbai. We had been allotted the possession pending OC in 2014, promising that the OC would be attained in couple of months. Further, to this the builder has applied thrice for OC to CIDCO and has been declined, for reasons not disclosed by the builder. Recently, a letter has been issued by CIDCO to the builder to get the premises vacated within a month , failing which action would be taken by CIDCO against MR&PT Act. We have transferred the entire consideration of the flat while purchasing it. The builder is asking us to vacate the flat immediately and comeback after OC. What are the charges we can file against the Builder? Further, can CIDCO take actions against us if we don't want to vacate. The builder is not ready to sign any legal documents. Also kindly confirm that is it required for the builder to be registered under RERA, since OC is not available for the property. Kindly advice the course of action.