Vani is right. But frankly, you can take solace in the fact that you aren't alone in such a situation. Many make the same mistake—mainly through overconfidence and an "I am always right" attitude. I know this hurts, but that's the fact. There's a saying in the Bible: "As you sow, so you reap."
And please note that "legally," TCS is right to take the stand they took. In fact, be happy that they didn't file any absconding case against you—they would have been within their rights even if they did.
Options Moving Forward
Now coming to the issue at hand, I can see you have two options. Please note that I am not going into the feasibility issues here at all:
1. Continue with your entrepreneurial journey—if not in the area you started with, maybe something else. But, just remember that "there's nothing called a free lunch in life." One needs to work like hell when on their own—much more than while in a job.
2. Restart your career all over again, forgetting you worked with TCS. You may need to explain the gap between your degree passing and the present as being on your own. Even though one would call this "bluffing/lying," I guess you leave yourself no other choice. Maybe there's truth in what someone said: "A lie needs an accomplice, a truth none."
I also suggest that you learn the lesson from your mistakes—you committed two mistakes, not just one by leaving TCS the way you did (the focus being on "the way" and not on "leaving").
All the best.
Regards, TS