Offer letter not being released

Hi All, I got interviewed with one of the Analytics based company in May month and got an offer via mail and salary breakup attached. I accepted the offer as the HR suggested to put my papers and he will provide the offer letter on June end(as my notice period was 90 days). But now when I'm asking for offer letter he is giving one or other reasons like we are not able to the stakeholder to take the approval as he is in client location. Did any one of you have faced this similar situation. If yes, then what should be my next steps.