Cognizant — filled cis form. but didn't get offer letter

Hai, i am manivasagan.

My interview location is
Tcs, thuraipakam, chennai (Oct 14th, 2018.) sunday.

I attended face to face interview. Cleared f2f interview for informatica on 14-oct-2018 sunday.

I cleared 2 rounds and also hr round.
And then i filled cis form.
Hr told me, "we will send offer letter with in 15 days". But still, i didn't get offer letter.

I sent email to hr, regarding sending offer letter.
But he is not responding to me.

Iam waiting for offer letter.

Could you please check and update me the status on this.

Interview place - thuraipakam, chennai

Regards
Mani