Phone calls with no ring, multiple missed call notifications, no vm

I have an iphone and have had the same issue as many others listed in the forum - 

Someone will call, my phone will not ring, but will show multiple (like 10 or more) missed call notifications, and will NOT go to voicemail. This happens for some callers, but not all. It does not, however, seem to matter where I am, or what time of day it is. It happens inside, outside, at home,  20 miles away at work, out of state, early in the morning, midday, late at night. 

I don't know exactly when it started but it's been at least 6 months, likely longer. 

From other similar tickets, it seems like there isn't a stable fix?