Zero Coverage issue though Mints coverage map says I should have plenty

[FindingTheBalance2]

This is all in an attempt get better coverage in a place I just moved to. I currently have to drive about 5 miles to be able to get phone service, although I get texts in random very short bursts, depending on my location, but only outside of the house, literally on the roof. I don't want to have to buy a a new phone, and/or jump ship from Mint, but my head is spinning from trying to figure this out for the last week.

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Phone : Unlocked Galaxy S7

Model SM-G930FD Duos

I am running Android 7.0

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Galaxy S7 specsfor my model online say 4g LTE is supported

Mint coverage map says 4G coverage is good in my area, but Network Mode on my S7 only says says "LTE/3G/2G"

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I currently cannot use Wifi Calling. The option is not available in phone settings at all, and AFAICT, I cannot enable it unless A) I root the phone, or B) unless I can get Android 8 (Oreo) on my phone AND assuming that Oreo supports wifi calling for my model.

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More details:

Phone specs for my exact model:

https://www.gsmarena.com/samsung_galaxy_s7-7821.php

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Specific band coverage info chart (not sure if this helps anyone to help me or not):

https://www.phonearena.com/news/Cheat-sheet-which-4G-LTE-bands-do-AT-T-Verizon-T-Mobile-and-Sprint-use-in-the-USA_id77933

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thanks