Legal help

Hi Dear Legal Advisers/friends! I am second husband of my wife and we both married on 15/05/2015 in front of house. She and her parents did not disclose the fact of prior marriage with mother's younger brother whose name is Mr. Kalloleppa Ogi and also hails from same village. I came to know this fact when I took her to enroll the Aadhaar card to Aadhaar center after 1.5 years of marriage and I inquired her about this matter, she said that she had been married to Mr. Kalloleppa Ogi while she was minor i.e. 14-15 years of age at Samuhika Vivah in her native place. She lived with him more than 1 year after marriage and she is not still divorced from her first husband, but her parents/elders are saying that she was divorced on 100 rupees stamp paper before village elders. After all of this, I collected first marriage photos from the place where the marriage was performed and I have copy of Aadhaar card as an evidence. I also inquired her first husband through phone, he also agreed that he had been married to this lady and lived with her more than 1 year. Literally she and her parents concealed this fact and I got cheated by them, so I wish to initiate legal action against them. PLEASE ADVISE ME HOW TO PROCEED WITH THIS CASE LEGALLY AND UNDER WHICH SECTION FILING OF ANNULMENT CAN BE DONE.