Bank and property

My uncle had taken 10 lakhs loan from a psu bank and he has mortgaged 15 lakhs property for the loan. My mother has given personal guarantee. Now my uncle is missing for 2 years and bank was harrasing my mother to repay the loan since my uncle had no wife or children. Now my mother has repaid the loan but bank is not releasing the property saying my mother is not mortgagor. Please help