Cognizant Technology Solutions — not received offer letter after one month

Address: Chennai, Tamil Nadu, 603103

I have attended the interview at cognizant on 28 july 2019 but not received offer letter yet. Got the call from cognizant to wait for some time but still no update. I have dropped mails but no reply from them.
All discussions have been done but still waiting for the offer letter. Don’t know how long will it take to resolve this. Waiting for offer letter.