[Addicted Young]

Ok so I have a very stange problem that was bugging me when my phone was pretty new. Just recently it has returned. I get random calls from an unknown caller. The time is random since it sometime accures in the middle of the night. Whats the weirdest part is that when it calls the thinking icon shows up and my phone completely freezes up. I cant answer or see who is calling. And there is no number to call back. Anyone have any idea what is going on or how i can get it to stop?