And, here come typical response -

telecom operators have informally shared with the department that the leaked information claimed in the ClouSEK report seems to be a compilation of old data sets of telecom subscribers and it is not due to any vulnerability in their system."

Source: https://telecom.economictimes.indiatimes.com/news/industry/cybersecurity-firm-claims-data-leak-of-750-million-telecom-users-dot-asks-telcos-for-security-audit/107244949