Cognizant — I have confirmation selection mail from cognizant but that organization is not giving me offer letter

Address: Pune, Maharashtra, 411027

Hi,

I have been selected in cognizant. Hr told me to releaes offer letter in 1 week after giving interview in cognizant. Its been 3 week i am not getting any update also respective person is not replying me on mail. My notice period is gonna end soon so i really need offer letter so that i can join this organization without any fail.

Please update me for my offer letter.