Capgemini — not sent offer letter yet

Address:

Mumbai City, Maharashtra, 400614

I am done with all my rounds, discussion with hr, finalized my package, submitted all documents but still i haven't got any update from hr regarding my offer letter as its been 3 weeks after discussion with hr. My interview took place in 12 january 2019 through walk-in.
I communicated with the hr via mails but always received the same response that "will call you".
I guess this is bit unprofessional and not expected out of such a huge company like capgemini. Can someone please help in letting them know that they shouldn't delay so much in providing the offer-letters. It's really maligning their brand image.