4G disconnecting ALL THE TIME for no apparent reason

[RoundRocks]

This is a last-ditch attempt before we disconnect our three lines and move to another provider since Verizon has not been able to resolve this issue.

I was added to my parents' Verizon plan with a third number in April 2021. My phone is a Galaxy S10+.

Everything was fine until 4G disconnecting ALL THE TIME for no apparent reason. When this happens, I cannot make or receive calls. The message "Not registered on the network" appears when I dial a number. (See screenshot: https://bit.ly/3EOHcv0)

By switching the airplane mode on and off, the network connection would be restored for approximately 15 minutes. It happens whether I am on Wi-Fi or 4G. It is especially frustrating when using Wi-Fi since I cannot know if I have lost 4G connectivity until I try to make a call.

This is not a coverage issue because: 

1. The SIM setting shows a good connection and I have 3-4 bars when this occurs.
2. This occurs even when I am driving and I have full bars.
3. My location has not changed over the past eight months.
4. I am the only one with this problem in my house - and Dad even has a 20-year-old flip phone.

We replaced the SIM cards and even reset the phone. My case was opened with a higher-up tech team and after a few days, I received a template response saying there was nothing wrong with my coverage. They recommended I buy a $250 network extender or a new phone, which is insane because as my observations demonstrate, there is nothing wrong with my coverage, and the S10+ is in excellent condition and has been functioning properly for months.

One band-aid would be to use an app such as Root Essentials, which continuously pings your phone connection and automatically toggles airplane mode for you to regain connection. The only problem is that it requires rooting the phone, which I am not a fan of, since you lose security updates and some apps might not work.

Does anyone have any app suggestions for automatically toggling plane mode when a connection is lost - without rooting? If not, we will disconnect all three numbers and switch providers (we want to be together).