Capgemini — Didnt receive offer letter after clearing the interview

I applied for release manager role and cleared all the interview rounds for the post. I had had the discussion with hr and he told me to give 9.9 lakh pa and told me that I would receive the offer letter next week. It has been 3 weeks now and today he is telling me that this role got filled internally. Meanwhile in between these 3 weeks he used to tell me that he is waiting for the approval. I don’t understand I this role was already meant for internal candidate why they took the interview and wasted my time my following up on it. I didn’t expected this from capgemini.