Cognizant — didn't release offer letter

Good morning.. Myself dipali aher, i have recently completed b pharmacy
Here i want to share one bad experience about walk-in interview at cognizant pune.
In month of november i had an interview at cognizant (Pune) for pv post. I have cleared all the rounds and told that i'm selected. The hr gave me a form to fill up about my qualification and contact details and told that i'll get the offer letter by email. I have tried to contact hr via phone call and emails but she didn't responded a sigle time, i haven't received my offer letter yet. We were group of arount 40 candidates who were selected out of them only 15 to 20 candidates got offer letter through email.
So, will you please help me out in solving this problem? What should i do now?
Email [protected]@yahoo.com
Please help me