Who called from 6477752828

I received two calls from that number and when I tryed to phone back, I was told this number is not assigned.
Both calls were made on my cell phone.

called to my cell phone - don't answer any number I don't recognize!  I presume it is a scam or someone trying to get money for something...

Just received a call myself to my cell but when I attempted to answer it the call disconnected.

Constant hang up calls. What is this all about?

Random call.  No voicemail left.  Read on caller ID as +64_7_775_2828. Strange.