I have been getting a call from 520-000-000000 too. I have not answered it and they do not leave a voice message. They have called me twice this week. I am getting really annoyed by it. I wish I knew why this is happening.
I also received a call from this number the area code is from Tucson and Nogales Az, they left me a me a voicemail in which they said they are a collections agency.
And that they needed my SSN and other personal info to provide me details luckily i do not owe anything otherwise they would have taken that info from me