some of my calls are being automatically forwarded? But my call forwarding is turned off?

I have No Idea What’s Happening? Some of my calls are being automatically forwarded? But my call forwarding is turned off? And when this happens I don’t always get a notification that someone tried to call. But there will be a voicemail (if they left one) that also didn’t leave a notification. At first I thought it was just one person having weird issues calling me. But now other people are saying they try to call me and it goes Straight to my voicemail. I even watched it happen on someone’s phone. They will get a notification or a voice message saying the call is being forwarded but nothing on my side? What is Happening?!