Cognizant — still not received offer letter

Address: Kolkata, West Bengal

I had completed face to face technical round (mainframe position) even hr discussions on the same day May 19, 2018 at cts tcpx kolkata . And i had received mail "interview status as select" and message " We will get back to you regarding the next steps shortly. Thank you for the interest shown towards our organization " cognizant talent acquisition team on May 29, 2018.

She confirmed that i will receive offer letter within a week. Still i have not received any letters or response from cognizant.

Why are you guys hiring every week or so ??