Phantom Ringing

My phone has been waking me up at 5:45 AM daily with the phone ringing. No user data is displayed and the phone app does not open. No record of a call is displayed in 'recents'. The ring tone is the same as I set up but rings more quietly than an actual call. No alarm is active or even set. I spent an hour on the phone with support that helped me update my phone (software update I advised I was not alerted to install) and reset it to factory settings. I have not dropped the phone which is protected by a case I purchased at the Apple store. During the time with support the phone rang 4 times just like described above every time the service was interrupted. I sure hope tomorrow I can sleep past 6:00 AM. I was not impressed with the 4 Apple Support calls following scripts and not listening to me.