Regarding cooperative housing society

We have a regd. cooperative housing society. One of the residents of the building had purchased a flat on the top floor adjoining the common terrace. It's not a penthouse since there is a common entrance to the terrace (appr. 600 sq. ft.) and the lift room and the overhead water tank are also there. However, the said resident perhaps with the earlier person i.e. the seller of the flat who agreed to mention in the Sale Agreement that 200 sq. ft. of the terrace though this flat is not shown as a penthouse in the BMC approved plan. Entire 600 sq. ft. It is shown as the common terrace only. Before buying the flat, the buyer never met any of the Society members to verify anything.with regard to the terrace etc. After buying the flat, he got it regd. by paying the Stamp Duty and the Regn. Fees. Subsequently, he sent the relevant documents to the Society asking them to transfer the Share Cert. pertaining to the said flat. The Society refused to transfer the Share Cert. to his name on the grounds that ths Sale Agreement was bad in law since he had included a part of the common terrace in the Sale Agreement which is contrary to the fact that no common area of the building can be sold or purchased by anyone or claimed by anyone as his/her personal property. The Society asked him to first provide a rectified Agreement for Sale wherein no area of the common terrace is being claimed OR a Statutory Declaration that he relinquishes his claim about the part of the terrace as mentioned in the Sale Agreement and that he has no right, title or interest in the common terrace of the building. He refused to give the same. Subsequently, he approached the Deputy Registrar's office asking them to direct the Society to transfer the Flat plus 200 sq. ft. of the terrace to his name. The Registrar's office after some months issued an Order accordingly. However, the Society did not transfer the same to his name and insisted that the buyer should submit to the Society as described above, before the Society can transfer the flat to his name. He did not submit the same to the Society. Subsequently, neither he approached any Court nor did the Society approach any Court. Now the situation is that he hasn't been paying the Maintenance Charges from Day 1 saying that he is not liable to pay the same since the Society has not transferred the Share Cert. to his name and hence not admitted him as a Member of the Society. According to him, he is not liable to pay since he is not a Member of the Society though he has been using and enjoying all the common facilities such as slights, water, lift, repairs, cleaning of the common areas etc. Lately he has been saying that it is not mandatory for a resident to become a Member of the Society, nor he is willing to become a Member. Kindly advise.