West Bengal Cooperative Society Rules - Nominee

My deceased wife nominated me to her owned flat in a Cooperative Society in Kolkata. The Society transferred the shares & interest in my name and admitted me as a member. Since, I do not have any family I want to nominate my 'Niece in Law' (my wife's only surviving sister's married daughter) as per Proviso under Rule 117(1) of WBCS Rules 2011 where a member can nominate anybody as the Nominee if he has no family. But, the Society says that my nomination is invalid as per Rules. Sir, please guide me how shall I proceed to register 'my Niece in Law' as my Nominee and how should I take up the matter with the Society.