Cognizant — offer letter delay more than 30 days

Address: Kandanchavidi, chennai, Chennai, Tamil Nadu, 600000

I had given an interview on 28th july, thoraipakkam, chennai. Cleared all the rounds of interview including hr round, salary negotiation also done on the same day.
I submitted my pan card xerox instead of my passport size photo. I was told to expect offer letter within 7 to 10 days.
But still i haven't received the offer letter. I got auto-generated select mail after that no update. I tried reached out to cognizant hr through mail, but got no response. Can anyone help me with hr contact or any advice appreciate.