I have a Samsung Galaxy S5 and a few months ago my phone started acting funny. First it shut itself down a couple of times, then nothing happened for about a month or two. Then a few weeks ago I was using my snapchat front facing camera and the screen started going black, then going back to the camera, going black, back to camera, etc so I exited out of the app and heard voices coming from the speaker on the back of my phone and it sounded like two young men (probably 20s) talking but I had no audio open or anything. Then today an event popped up on my phone that was in my calendar that said "How are you doing?", but I didn't put it there and my phone has a passcode so no one else did either. I downloaded my system update yesterday so it might have been that but I'm not sure. Either way, should I take my phone to someone to get it checked out? Do you think I've been hacked/tapped?
Sorry for this is so long, I'm just really weirded out.