Since October when I updated to iOS 12, my iPhone 7 started having issues with phone numbers that may or may not have the country code (+1 for US) saved to their contact. The majority have been SMS and MMS messaging including group chats. However, it occurs with iPhone numbers or iMessages as well. Randomly, it will not recognize a phone number as being a saved contact. It will also not recognize My OWN NUMBER and I will receive my own message back to myself--so regular two way text messages because "3-way group chats" between the recipient, myself, and myself. The contacts are saved in the icloud, but I tried switching them to other locations--on the phone, google account, etc-- and there was no difference.
When this first happened, I thought it was an iOS error-- so did Apple who I contacted back in November. They assured me their engineers were working on it and an update would be coming to fix the problem. 9 months and iOS 12.3.1 later, they are now pointing me towards Verizon for assistance. I've done soft resets daily to weekly to monthly, I've reset my network settings, I've done factory resets from backups, and started completely from scratch with full data reset. AND IT STILL KEEPS HAPPENING.
I don't know what else to do. Any ideas?