the father's clan

I received an e-mail today for breaking fasting event from a company. I am usually receive invitation, but this one is kinda different from the others. It had my name on it, it wasnt strange if they only named me "Efi" instead of "Efi Yanuar". 

I couldnt recall if I ever had written my and father's name on their guests book. strange. how did they know it?

my real name doesnt have my father's name, so it is like I promote my father's clan