Cognizant Technology Solutions — did not receive offer letter

After long interview process, i cleared all the rounds. I was informed that i will be receiving my offer letter within a week but i have not heard anything since then.
Wrote numerous mails but nobody is replying to my mails. Please let me know how do i proceed further.

How do we get hr email i'd or how do we know if our position went on hold. If those people are not recruiting at least they should give feedback and make candidate aware.