Cognizant Technology Solutions — regarding delay in joining letter

I had given the interview on 30 november 2018 in galgotia university greater noida and got shortlisted and received the mail of shortlisting on 2 december 2018. On 11 december 2018 i got the offer letter and further i uploaded all documents and got the acknowledgement too after uploading.
And on 22 december i got an mail that one of my document is pending that is my btech marksheet. And i uploaded the same on the same time after receiving the mail. And got the acknowledgement too.. Further i don't have any information regarding my joining letter... Can anyone hlp me this situation how much time will more taken.. For joining letter?