Who I have the same questioned this topic

I use Family Base on my phones on my plan.  On my daughter's phone, she keeps getting phone calls from "0".  Durations like 15 minutes, 27 minutes, 11 minutes, etc.  I have it flagged as a contact that I watch and it shows up every couple days.   She swears no one is calling her.  I believe her, because some of the calls show as coming in at a time where her phone is restricted from receiving calls.  Additionally, when I just look at the call logs on the straight up Verizon site there is no record of these calls at all.

So, what's up?  Who is "0" and why do they keep calling my daughter?