illegal termination

I was working with MNC from last seven years as a Design engg with good performance. I was terminated on 1st June 2018 and there is no reason given for my termination. It mentioned only as discussed & as per contracts. The appointment letter contains the clause of 2 months notice period. I registered the ethical concerns on the company portal about my delayed promotion and nepotism going on in company in April 2018. The investigation was started by the same office against which the concerns were raised and breach of confidentiality took place. Although company is committed against the zero tolerance against retaliation they did it. They were forcefully asking me to resign and when I denied terminated me and asked me to leave the premises within 10 min. I have not signed any of documents including receipt of termination letter. But the dues were settled with a lightening speed within a week to cover up he matter. When I approached Global Ethics and compliance committee for this unfair and illegal behaviour they appointed the investigation team. I have submitted the documents related to my performance, appreciation from
client, and unfair practise by office head in appointment to his relatives and preferential treatment. They kept the investigation report pending from 1.5 months and now come out with that my allegations was not substantiated. I am feeling cheated.
I have all the documents related to my performance which could be supportive that the performance was not the reason for my termination.
The company HR policy mention the At will Employment, in which termination can be done without providing any reason. Its the act of retaliation against whistleblower which company shying to accept because of stake at its reputation.
I sent the legal notice to them as well which they not responded. What options do I have further?