Builder completed 50% of construction now harassing me

Sir, I entered a collaboration agreement with a builder to construct a 4 storied building on my plot against one floors. Builder disappeared after 50% construction. Builder had entered an Agreement to sell with an individual who had agreed to finance rest of the project and after construction i have executed a sale deed in his favour in delhi. Now one of the financers of builders is harassing me on the pretext that he had an agreement to sell prior to one whom i sold with the builder of the same floor of which i was not aware and has filed a civil suit. Please advise my defence