Issue of duplicate share certificate

In the AGM whilst scrutinising the resolution for transfer of flat, I observed that there were two share certificates with same cert.no. (One looks like a coloured xerox copy which looks like original) One member then said that police case should be resgistered. The Chairman and persons who had signed one of the certificate on approving the transfer said they will ask the owner to produce a xerox copy of the share certificate which is lying as mortgage with the bank. But nothing was done. Now the present transferee has sold the flat to another person. Now this person is approached the society for transfer of flat in his name. The Chairman asked me to come to the Committee meeting for approving his transfer. I have resigned from the Managing Committee as the Secretary was not following byelaws and they have already appointed without consent for DSEC the new member. I have refused to attend the meeting as I told them that I am none to authenticate the correctness of the share certificate. What is the correct action to be taken so that I can tellthe Managing Committee the right procedure.