HCLTech Sr Software Engineer interview questions

Interview process consist of 3 technical rounds and then HR round. First technical was face to face , very basic questions have been asked and it's not big deal to clear. Second technical, was telephonic within their premises. It was more detailed one. Later on they told me I'll be getting a client call for last technical round. After clearing client round, there is HR round. Even after clearing all rounds of my interview, I've not get my offer letter. I've followed-up with HR till almost a month but nothing helped.