In case you didn't figure this out. I was strugglin with this too, but I ran across your thread plus the thread below. I couldn't figure out what was triggering it. But it will always re-dial the last number you used to S-Voice or Google search to dial for you. Like poster number 2 suggested deleting your Davlik cache may do the trick. But since I already had
CCleaner installed, I gave that a shot. Like the thread below my phone would redial everytime I turned off/on location services. After running CCleaner no more issues. BTW, I'm on an S6 Edge w/ marshmallow.
http://forums.androidcentral.com/sam...ad-happen.html