Change from premium to family

[lgdic]

I have a premium account and my father has just made a family account. He invited me to get a member of the family account just as he did with my mother (she didn‘t have a spotify account at all) and my sister (she had a non-paying account). With their account everything worked out perfectly but I didn‘t even got the e-mail. How is that possible? How can I also get a member without loosing my account?