Cognizant — offer letter not received for interview on 6th oct 2018

I attended the interview on oct 6th 2018 and got a positive response. Even package discussion is also done with hr on the same day itself. Post that i received cis form mail too and also replied back.

My last contact with hr and i have tried contacting him through mail/call, even later 4 weeks i didn't get any acknowledgment from him.

Could you please tell me what should be my next step and when can i expect the offer letter.

Also, my notice period keeps on reducing. My last day at the current organization is 04-march-2019 (I can make it 10 days before also). Even am ok with 9/9.5 lpa expected ctc.

I am eagerly waiting for cts offer letter.
The opportunity of working with cognizant and exploring more will be my pleasure.

Kindly response asap.