Cognizant — HR is not renewing my offer letter

Address: Chennai

Hi.. I received offer letter from Cts. But, when I asked for renewed offer letter with new DOJ, they are refusing to help. At the time when I received offer which happened 2months before itself, they specifically asked me to contact them in this month to get renewed offer letter with new DOJ as I informed them at my notice period ends only in this month and due to which they gave me temporary Doj for this month with with some random date on which I won't be able to join for which they said I can contact them in this month to get renewed offer letter with new DOJ which I believed. But the fact remains that the HR gave me false promise of helping me. How to resolve this situation.. Is there any complaint related email address with Cts to address such issues?