Builder missing ex-owner of the land asking his land back

I want to get advice if i had deal of purchasing house with the builder. In that extent i payed ample amount to builder in cash and entered into contract with plot owner mr a nd builder. But builder went on misssing and incomplete project. I construct house with my money on plot, but since i paid 50% with dispute nd couldnt go there as of far distance. Ex-plot owner mr a sold my house without my acknowledgement to other party. Now plot is owned by me but mr a took sum amount from other party nd didnt paid me nor inform me.?? I want to resolve dispute, not interested in plot nd want my money back what legal steps i should follow?? If mr a is saying that he is insolvent how can i recover my money which i had paid to builder if i had recceipt as well as legal documents for plot nd mr a has also sold without my concent??