Cognizant — I have not received offer letter

Address: 560076

I have been selected for Programmer Analyst position on 15th April after clearing the technical interview and HR discussion and I have been told in HR discussion that I will receive the offer letter within a week. I received an email from cognizant for photo upload on 17th April and then an email of confirmation from cognizant that i have cleared all the rounds of interview on 26th april and then i did not hear anything form them. I tried to get answer from an HR from whom I got the call letter through email but she did not respond. There was no phone contact given. It is going to be 3months now but no sign of offer letter. I feel I have wasted my time for the whole interview process of Cognizant. I am thinking this how a company treats its potential employee.