builder ran away after i gave money. advice needed!!

I gave 8 lakhs for a flat. The builder, who was brought into contact by one of my neighbours , gave fake address in the stamp papers. I went to his house but he already ran away. My neighbour gave us guarantee too, but now he also runs away whenever he encounters me. It has been 10 years already and 8 lakhs in vain. There is also no registration of the name of his flat. What should i do ?