To answer very definitely to your question that whether your marriage is null and void or not, it is important to see those papers, which you signed at the time of so-called marriage in the premises of NGO.
On the face of it, the marriage appears to be null and void for the following reasons:
1. The marriage has not been solemnized as per Hindu customs and rites as only garlands were exchanged and there was no saptapadi around the holy flame and seeing the "Arundhati" star. These are, as described in some judgments, are two most important ingredients for declaring that the marriage was solemnized as per Hindu rites and customs.
2. The marriage has not been registered either under Special Marriage Act or Hindu Marriage Act. I am quite sure about this. The reason behind this is that either under special marriage Act or HMA, the bride and bridegroom's presence before the marriage registrar (marriage officer) is mandatory. As you did not present before any marriage registrar / marriage officer, your marriage has not been registered.
*here I mention that as per HMA, registration of marriage is not compulsory to make marriage valid. But your marriage is null and void for the reason I explained in para 1 above, in addition to the following most important reason.
YOU AND YOUR HUSBAND BELONG TO PROHIBITED RELATIONSHIP UNDER HINDU MARRIAGE ACT AS WELL AS UNDER SPECIAL MARRIAGE ACT. There is only one exception to this is that if in your families such custom exists a marriage can be solemnized with mother's sister's son, then it is valid marriage. You both are cousin brother and sisters. Even in Tamil Nadu, Andhra and Karnataka, as far as I know such relationship does not exist between the couples in Hindus. So, I safely derive that this relationship is prohibited relationship and it is null and void.
Now, what can be done, if the marriage is null and void:
1. If the facts are as I said above, then withdraw the divorce petition with a liberty to file an appropriate applicatin under appropriate provision of law for declaration of marriage null and void, if advised so.
2. You can self declare that the marriage is null and void and also issue a legal notice to such an extent to your so-called husband and can go to do whatever you like ( I mean that you can go for another marriage. But your husband will not sit idle and file a case against you for bigamy and againnst your new husband for adultery. Do not worry. There you have to prove that your first marriage is null and void for the reasons stated above).
3. If you want to avoid the ill consequences as narrated in para 2 above, you can file petition for declaration of your marriage as null and void. Once you prove your facts, you will get such decree and from there on you will be free.
Wish you best of luck.