Cognizant — regarding joining date

Sir/madam,
I have attended interview for programmer analyst role on december 16-2018 for cognizant off-campus at cbit college (Hyderabad) after 2 days i got mail from talent acquisition group that i am shortlisted then after two days i got offer letter then after some days i got pan card approval message but till now i did'nt get doj as my expected doj os 10th jan 2019 but till now i didn't get.
Some of my frnds got doj and they joined also, when can i expect my doj pleasee solve my problem.