My iPhone calls people on its' own

Hello,

I have an iPhone 5s 16GB. It is around 8 months old. I live on a floor of many college students and for a while now, my phone has been calling people who live on my dorm floor on its' own. During this time, it has been running on iOS 8.1, 8.2 and 8.3.

I will be asleep and my phone will be calling people on its' own. It probably sounds like I am crazy, but I swear, this is true. When it happens, it shows a missed call from the person it calls, not an outgoing call. The other person's phone shows an incoming call from me. It's driving me crazy!!!

Help!!!