Cognizant — fake offer letter

Address: chil sez it park keerthanam ,saravanapatt, Coimbatore, Tamil Nadu, 641035

I have applied in naukri for job opening. And received a call from hr named arun kumar from cognizant. He interviewed me and selected me for programming analyst. He sent me the offer letter with cognizant letter head from [protected]@cognizant.com

After which i din get any joining kit. I phoned him and asked when to join and whom to be approached. He said he will send me all details in email but i dint receive one... Further which his phone is switched off for long.

When i come to it park. He didn't allowed the cognizant, they said i have a fake offer letter, then how come i received email from a genuine cognizant domain...