You have paid the full price, and the vehicle is not registered, hence you have the full right to ask for other vehicle if after PDI you are not convinced with the vehicle. You can even ask for a full refund in extreme case. Car is in workshop for 3days? For a job that requires 4-5 hours max! This is a very sour experience. Just tell them that they are either alotting a new piece or a full refund, have these communications on mail and try to mark the tata regional manager on the mail.
Just when Tata products were starting to hit the ball out of the park, Tata sales people have gotten Casual & Overconfident, just like a decade back when they were selling indicas and indigos in high numbers. Recently many prospective buyers have experienced sour attitude from sales team, feels sad from a Tata customer point of view, here we encourage our known ones to go towards tata and the showrooms act completely opposite.