As per your query,
If the new builder entered into agreement with new buyers with out cancelling the previous agreement of the old builder is void abentio . The new agreement is not legally sustainable in eye of law.
The State Government of Maharashtra acquired the agriculture land in the area of Navi Mumbai to set up a new town and entrusted the same to CIDCO, as the Development Authority, for development and allotment of the plots under various categories. It is the responsibility of CIDCO to arrange all such approvals before allotment of the plots.
CIDCO is a wholly owned company of the State Government and is designated as a new town development authority for the town of Navi Mumbai, which, initially, issues an allotment letter with the condition that after the payment of the last installment or the full sale consideration, with miscellaneous charges as mentioned therein, an agreement for sale will be executed and registered in favour of the purchaser within 15 days of the possession; whereas in case of Societies, there is a provision in Article 25 of the Bombay Stamp Act that such a document by the Society attracts stamp duty and after the amendment of the Indian Registration Act in September, 2001, such a deed has to be registered. Therefore, the Banks and the Financial Institutions are advancing loans in cases of CIDCO properties on the basis of the allotment letters with mortgage N.O.C. in their favour.
Check the whether your flat was sold earlier or not in record of Sub registrar office .