I am using an iPhone 11 Pro, but had the same problems with iPhone X, before I upgraded the phone.
I have two issues and it may be because I enable the WiFi on the Phone settings:
1. All incoming calls are sent to voicemail. I do not get the call; just a notification when a voicemail is received.
2. I am getting up to 10 duplicate messages from senders not using iMessage.
I have been to the Genius Bar with Apple and no success. I have also filed an open ticket with Verizon but have not received a solution. I have reset the network several times, re-installed the iOS software, and even replaced the WiFi devices. Still no success.
Any help would be appreciated.