Air India - Cheated and extra baggage fee collected

I had a flight from Chennai-Delhi-Chicago-Raleigh on Feb **th (*-**PM). It was part of a round trip flight from Raleigh, which I had used to get to Chennai on Nov **th. On the journey from Raleigh to chennai, the first carrier was United Airlines, followed by Air india. Since united doesn't allow more than * **kg check-in (I had * **kg check-in), I was asked to pay ***$, which was rightfully written on my ticket as well. But the return journey was where I got cheated by air india in chennai. My ticket clearly mentioned that both my **kg check-in baggages were FREE, but the air India lady at check-in kept forcing me to pay RS.***** (***$+tax) as fees. She asked me to show my ticket to prove that I was allowed * free check-in, and when I showed it, she kept saying it was incorrect and that I was wrong. She simply refused to listen or allow me ahead, and she forced me to either pay the fees or she would throw the luggage away. I am a student, and needed to get back to US, and after some argument I was forced to pay. Initially she demanded cash, but luckily I had my indian debit card and had to pay the amount of Rs.*****. A month earlier, while double-checking all my ticket details, an air india support employee had explicitly told me that both my luggages were free. I even showed my student id when she asked me to prove it, but when I showed, she still forced me to either pay or getting the luggage thrown away. Everytime I showed her proof she asked, she literally discarded it. She even called another employee on the phone and was making fun of me in tamil, assuming that I did not know the language. Thus, I faced total mental harassment as a student, and suffered huge financial loss of my hard earned money. I would strongly request for a refund of the full amount back to me, and hope such incidents don't take place again in the future.