Sale deed with notary

I have purchased a flat fm a builder and entered with him with SALE DEED duly Notorised.  i have paid half amount of agreement.  suddently the builder sold the same property with other customer who paid the Stamp Duty too with a intention to gain higher amount.

will i fight for the possession of my flat .  I have not paid the stamp duty , will it be a hurdle in getting back my flat?

Plz help out me.  Thanks

SHEKHAR NAMA

9850097222