Chargebee Advanced Solutions Engineer Developer Support interview questions

A total of three rounds. - Technical round to access your coding skills. - Hiring manager round. - Culture fit round. The first two rounds went really well and the interviewer of the first two rounds were really satisfied with my answers. Third round - I almost gave honest answers to all the questions asked. He also looks convinced. Everything went really well BUT the very next day i got an email saying that I was not selected which is ok. I tried reaching the HR asking for reason on why i was not selected so that i can take that as a feedback and don't repeat in the next interview. But i was not able to contact the HR after that. No reply for emails, no answers for phone calls. This is really disappointing. We are OK if you don't select but at-least try to give a honest reason.