I second Steeroid on the Legality Aspect .....
When you have all the Records intact and have enough proof that your vehicle is a Lemon, You should go to the Court. Just File a Case and send out a Notice, I dont think you will need to fight the Case cos i am sure they will come forward for a Settlement.
Once the Case is filed, Legally you have every Right Broadcast to a Much Wider Audience (read Newspaper's). That should give Tata's enough Publicity and prolly Teach them a Lesson as well. The Flip Side to it is probably Mr Ratan Tata will read it in the Paper's :-).
PS : When u are e-mail'ng Tata's Personnel (or any Large Coporate for that matter) refrain from using Free Mail Account's Like yahoo, gmail, hotmail etc..... These are treated as Spam most of the Time.
Generic ID's like
Support@tata.com etc.. are however excluded from the Filter.