Who I have the same questioned this topic

I was trying to buy an iphoneX through the apple store website. When they ask to input the verzion account information, I tried combination of "my phone number + zip code + my last four ssn", "my phone number, same zip code, my account holder's last four ssn digits", "my account holder's number + zip code + my account holder's last four ssn" and "my phone/my account holder's phone + zip code + the account pin number". And none of that combination worked! I feel like it should not be my last four ssn digits because I never gave Verizon that information. Any idea? I am in a family plan.