Money disappear on my mother account

Hello Peter My mother she was having an account with standard bank just to save a money because she was using another Bank My mother passed away October 20 before she passed away she sent me at standard bank Vryheid because everymonth she was receiving some strange massage that shows someone is using my mother account that time she was having R50 000 + on her account around September when I arrived at standard bank to ask about my mom money as she asked me to go to ask at standard bank the person I found there she told me that nothing happening on my mother account but when my mother passed away October 20 the following month we found that R26 left I want you to help me to found out what happened with my mother money at standard bank