In this case the 2 interviewers were partners. I could also send mails to them instead of HR, but not sure if it is a good idea to bypass HR. you tell me.

Thank you for your answer Francesco, it is actually the only answer I got that makes sense. I will now be on the hunt of that competitor offer.

In the past they have been very responsive, so I do not see why this could have changed overnight.

In my question I worte that I had already called HR, and they had promised to get back to me on the same day. But there was no call.

After calling HR twice and getting no response, I met the company in a career fair, where a consultant took note that I had not received feedback. A week later (4 months after the interview), an intern from HR called me and apologized for the delay saying my application process papers may have been misplaced. Then he went on to give me feedback about the case (which I barely remembered by that time). Very unprofessional the way they behaved, particularly because I made contact with HR on repetitive occasions and they did not contact me back. I did not expect this from BCG and honestly I got very disencouraged from applying there at a later point once my professional experience increases.