Cognizant Interview Question

All the interview questions were basically on Core Java, multithreading, microservices, Springs. My interview was scheduled at Cognizant through a consultancy (shell Infotech). They called me for the interview process. I reached the venue 20 minutes before the interview process, Meanwhile, I got around 3-4 calls from the consultancy to confirm my presence as if the Cognizant panel came just to interview me. As I reached, I realized it was a walk-in process which was not being told to me by Shell Infotech. Anyhow, I moved ahead and cleared two rounds of technical (one face to face and one telephonic in which a manager took my process through the Cognizant intercom) and the third round was with HR. I was being told that I have been selected and have to mention my expected compensation. I stated that I was already holding an offer and after listening to this, Mr Hemant (from Cognizant HR, Gurgaon) told me to send the offer. I told him that it was not their business and they should either say Yes or No to my expectation to which they stated that we are proceeding with your candidature, and you need to send few documents like the Adhaar card, pan number etc. I reached home and mailed my documents. I had a very bad experience. Since then I haven't heard any response from them. I contacted Shell Infotech for the same to which they said that we are trying to reach Cognizant people and we will get back to you, the second time I called them, they said we are on lunch, will give a call after lunch. But they did not call back. I had the Cognizant HR's email id and contacted them for my offer to which they replied that we are not proceeding further with your candidature as you have not provided the offer letter.