Sporadically missed texts/calls + "Not registered in network" + Terrible Support = Severe Problems

Problema

My phone is sporadically unable to receive text messages and phone calls (appears out of network for the sender/caller) even in the areas with great signal reception. When the phone is in that state, I am also unable to text and make calls: a "Not registered in network" message appears. The internet connection does not disappear. I can even be watching a video in great quality using my mobile internet, while for someone who tries text/call me, I appear out-of-network.

Restarting my phone, fully recovers the ability to call and text. I even receive SOME missed text messages that were sent to me while I appeared "offline" often in messed up order and minutes apart. However, some of the texts never reach me which makes things even more confusing.

I can’t tell for sure what triggers this state, however, I noticed that it happens more often when I drive around the city. 

The critical issue is that even when I hold my phone in my hand actively using internet and watching videos, I have absolutely no indication that my phone is unreachable by people until I try to call or text. Since I don't frequently initiate calls and texts, I realized that I sometimes ended up with days of a "disconnected" phone. While most of my communication goes through internet, those less frequent, but most important new personal and professional connections happen via phone calls and texting. It's just recently I realized that over the course of several months if not years multiple miscommunication issues I had with important people were caused by this 'auto-ghosting feature' T-Mobile effectively enabled for me without asking or informing me. Please see "Problem Severity" below.

I suspect that it might be related to the fact that my phone does not support 5G and to the Voice over LTE feature T-Mobile introduced some time ago. I do NOT need 5G at this point, the internet speed is satisfactory.

My phone is a factory unlocked Samsung Galaxy A8 (2018) SM-A530F/DS purchased from the Samsung store on Amazon in Sep 2018.

T-Mobile Support was Terrible

First, I brought my phone to several T-Mobile offices in Boston area. No 'expert' there was able to find the cause of the problem or fix it. Then I called the official  T-Mobile tech support phone number, took time to explain my problem, they said a more tech-savvy engineer will reach me out within 72h (!). And they simply haven't.

Problem Severity

This is a very serious problem. As I am discovering now, it has affected my personal and professional relationships over the course of months if not years. For people who try to communicate with me, it appears as if I am ghosting them. From my side, it appears that people ghost me.:

• They try to call me and they know I am home, but I appear out of network as if I blocked them or turned off my phone
• They send a text message and it never reaches me.
• I expect a text message from them, never receive it, and forced to think negatively about the person

At this point, given that my issue was not even addressed by tech support, I am considering legal options to solve this problem. It's not that T-Mobile was just unable to deliver the service defined in the contract, the service effectively imposed major damages on me, including damages to and loss of professional, financial and personal relationship opportunities. I am in the process of collecting records and witnesses to support my claims in case of a potential legal action.