Municipal Corporation Of Delhi — Is your birth certificate is school property?

Address:	New Delhi, Delhi, 110085
Website:	about school authorities

Respected sir/mam
I want to ask you general information about birth certificate.
I want my birth certificate back from school authorities after leaving the school but they said that my birth certificate is their property.
How can this be possible? Birth certificate is a government paper and how it can be their property?
Kindly let me know if this is true.