Cognizant — offer letter not received yet

Address: Chennai, Tamil Nadu

I have given interview for mainframe and got selected on 9th of march 2018 at cts okkiyam, chennai. After the hr discussion, i was told that i will receive my offer letter within next 4-5 working days. On 17th of march i received a mail to upload my photo from cognizant talent acquisition and i did the same in that day itself.
It's more than 45 days now and still i didn't get my offer letter yet.