Dear Shrimani,
Your case needs to be handled under the provisions of Indian Contract Act (ICA), 1872. Since you are/were not employee it cannot come under the purview of labour laws.
Under the provisions of ICA, appointment letter is a contract between employer and employee. However, you were issued offer letter and not appointment letter. Therefore, the contract between the two parties not legally established. Nevertheless, offer letter is provided to enter into the main agreement. Should be it also construed as contract? Answer depends on how court interprets the law.
Section 4 of ICA, 1872 deals extensively on acceptance of offer whereas Section 5 on revoking of the offer. The primary consideration is whether you had accepted the offer letter, how did you accept it, when other other party came to know about the acceptance of the offer and after what time span the other party revoked it. Did you suffer any financial losses because of revoking of the contract? If yes, do you have evidence?
I recommend you approaching a lawyer who handles cases under ICA and explain your case. Do not approach lawyers who handle labour cases.
Thanks,
Dinesh Divekar