1. Since the Society has already issued NOC stating no due for the said flat, it can not claim any outstanding now,
2. Pay the claim since the society will not allow you to register the flat in your name,
3. After that file a complaint case against the seller making the siciety as a party alleging deficiency in service and unfair business practice claiming refund of the amount, damage and cost,
4. Complaint against the society may not be considered as a fit case to be filed under Cunsumer Protection (Amendment) Act,2002 since society is not tye seller in your case.