I sold my existing flat and we Registered the Sale agreement on 6th march (registration complete). T

I sold my existing flat and we Registered the Sale agreement on 6th march (registration complete). The Society secretary was not co-operative to give NOC but finally gave but then has declined to sign the Bank's Lien Letter that requires the Society to Mark a Lien on the Flat and confirm that the Buyer cannot sell it without Bank's permission. nThe Secretary is not issuing this Letter stating its a Legal Issue and needs to consult a legal advisor. We requested him to consult at the earliest, he is only wasting time. The Buyer of the flat also has time limit to shift to our home as he is staying on rent. We requested Secretary several times to co-operate & take the necessary opinions, but when we went he banged the door twice on my senior citizen parents face telling us he will do it when he wants. He then wrote to us stating he will take legal advice, and also committee meeting and will have to inform all members in AGM. Our Loan disbursal is pending because of this, what can be done?