Land Dispute Issues

Hi, I bought land by an agreement with the seller(C) measuring 50ft by 47ft in a certain suburb. The seller gave me the original agreement he had exchanged with the original vendor. I immediately constructed three boys quarters and a pit latrine. After some three months, another person(B) came out with an agreement showing that he had purchased the same plot but measuring 47ft by 61ft from the same seller. The seller disappered but latter was caught by B and was imprisoned. The police charged him by obtaining money fraudulently from me claiming he had no right of selling to me since B had already bought. B came to me claiming i should vacate the plot. I opened a civil case for trespass against B who in his defence wrote that I accepted C's fraud and sued him already in the criminal court and also counterclaimed trespass against me. Kindly advise how i can win such a case. The measurements are different, I already built a bigger house and am staying there. I never took C to police but the criminal court records show that I was the complainant. I will be grateful for your advice.