Legitimation allows illegitimate child to use father’s surname

Dear PAO,

I went to a government office for the purpose of securing an identification card (ID). I was told that I still need to secure additional documents aside from my birth certificate if I want to have an ID with the surname of my father in it. I got really confused because although I have my mother’s surname in my birth certificate, I have been using my father’s surname ever since my parents got married, seven years after I was born. What should I do about this?