Transfer Fee for purchase of flat

I have purchased a flat from the first owner when the society was being managed by the builder and not handed over to the residents. The "No dues pending" and "NOC" was issued by the builder to the first owner and submitted by me to the bank for approval and sanction of my home loan. The builder also issued NOC for transfer of MSEB Electricity meter to my name after which I have got the same done by applying to the MSEB.

Now the society has been handed over to the residents. The managing commitee has been formed. Now the society is asking me to pay the transfer fee of Rs. 25,000/- for the member-ship of the society. As per my understanding with the seller of the flat was that he will take care of the transfer-fee and all necessary documents required for the sale of the flat.

The builder has not shown the transfer fee in the account statement given to the society. The builder representative is verbally saying that they have not received / collected any transfer fees from the seller. The society is also not making any efforts to collect the same from the builder. They have issued a letter to me saying that I have to pay the transfer fees of Rs. 25,000/-

Am I legally respnsible for the payment of transfer fee to the society ?

What is the society bye-law regarding the same?

Is the society's stand correct in this situation ( not recovering the transfer fees from the builder but asking me to pay the same) ?

If legally I am not responsible for the payment of this transfer fee, what legal alternatives do I have to protect my interest and obtain membership of the society?