Transfer of Share certificate in case of death & missing cert

Hello, My father had purchased a property in mumbai, we had the share certificate too in my father's name. My father passed away about 10 years ago and he had not done any nomination. We wanted to transfer the share certificate from father's name to Mother's name. The secretary of the society asked us to submit the original share certificate and misplaced it all in the name of transfer. We have sent several letters to the Society for transfer of the flat but have not got the Share certificate.(original too) When we enquire about it we are told it will be given to us soon. This is going on for 4-5 years now We are living in this flat for past 16 years and paying maintenance and other bills in my mother's name. Now they are asking us to submit a letter saying that we misplaced the original share certificate. We don't have any written proof justifying that society misplaced the certificate. What should we do in this case, all we want is transfer or issuance of the certificate in my mother's name.