I am very sorry that you had such a difficult time with Synapseindia. It seems to me however that your complaint should be directly with them and not Elance as I can't for the life of me, figure out why you are mad at them. I don't work for Elance but I have used Elance in the past to find all sorts of providers, writers, lawyers, graphic designers, and programmers and have not had any issues whatsoever.
Like you, I not only use review the feedback and reviews of each provider I choose but I thoroughly interview each provider using the PMB board and I also make each one sign a contract before any money is paid. In your instance, it seems as if you did use the feedback system but still had issues.
Perhaps you need to take advantage of a mediation service or hire an attorney to assist you as I am a bit unclear as to why you aren't happy with Elance. Perhaps you wanted them to do more? But honestly what could they have done in this instance as your beef is with one of their providers, not them directly.