This # is calling my house in the middle of the night every 15 minutes and there is only a buzzing sound when I answer,

I have been called 9 times since 6:06 yesterday afternoon, December 7, 2011. The message recieved constantly is of an offender being released from custody. I don't know the person being released. My guess is my number on my cell phone belonged to some one else once. I've had this number for two years.