I have a strange problem. When someone calls, the call goes to VM. The phone rings like a half a second then goes to voicemail. Do Not Disturb is off as well as Silence All Unknown Calls. I have erased all network settings. You name it, it has been done. AT&T "fixed" it a few days ago, but now the problem is back. I am on the current ios: 15.4.1. Is this some sort of hack/virus/spyware?