I have a Galaxy S5. Sometimes someone will call but my phone sends them right to voicemail, it doesn't ring on their side or my side and I'm not notified that I have a voicemail from them, nor does their call show in my call log. I find out they called either by randomly checking my voicemail or they text me and ask why I'm not answering (on their call that I'm expecting). It does it to 4 specific people that I know of and these people are in my contacts. It doesn't always do this, sometimes the call comes through, sometimes it doesnt. It did happen one time when my then 13 yr old son called me from the library and needed me to pick him up way earlier than we had planned. I had no idea that he had called until he walked through the front door and asked why I had turned my phone off, cause his calls went straight to voicemail. My phone was on that whole time. Not only is it an inconvenience, I'm scared I may miss a family emergency type phone call. Does anyone have any idea why my phone does this and how to fix it?