My Samsung Galaxy Note 2 was just randomly ringing! What do I do?

[Art_Gamer001]

I couldn't fall asleep so I decided to use my phone (Samsung Galaxy Note 2). I had my ringtone, notifications, and system volume tuened off but media at one because I was watching YouTube. After an a hour or two my ringtone started AS LOUD AS POSSIBLE! No "Incoming Call" pop up at all... I was SO startled...so I quickly turned it off BUT IT KEPT ON GOING! So I had to turn it back ot and shut it down...I I am so afraid of it happening again. What should I do? Oh and I Don't have a cell phone plan.

 

[Art_Gamer001]

I'm still shivering...