Hi. I don't have surname or last name in my name and while filling TCS nqt form it was mandatory to full both first and last name. So in the last name block I filled NA. Now I got an offer letter from TCS which I accepted. But i am afraid if the name issue is going to create any trouble in my joinin

See this is a legitimate problem which can put you in trouble. But while reporting, you should keep all the documents such as application form print & all the NQT related documents (available to you ) soft copy. IF asked you can explain why the error occurred & in most cases such discrepancies can be ignored although its dependent on the authority at the reporting desk. So go for it & what happens. Don't get nervous else you should make a good convincing reason in your mind so that if any of the officials ask you anything, you can articulate the reason with confidence.

I wish your problem get resolved soon. All the best!