I understand the issue with your Samsung Galaxy J3 not working would be frustrating. At this point, if a factory reset doesn’t fix it nothing short of flashing the phone will work (and that won’t be enough if it’s a hardware error).
Since you’ve been a long-time Republic member; you might like to know that unlike your previous Republic phones (which used modified Android operating systems to make Republic’s blended WiFi/cell service work), your J3 and all Republic 3.0 phones do not use modified operating systems. They are the same North American factory unlocked phones used elsewhere. If it was an operating system update that caused this situation, that update came from Samsung not Republic.
To the extent there is a silver lining here, it’s that your 10-month old J3 is within the one-year manufacturer’s warranty, giving you a potential warranty claim. You will, however, need to have that conversation with Samsung. If you wish to do so, contact information is here: https://www.samsung.com/us/support/#contact_us_for_support.
Another potential option would be to see if your local Best Buy has a Samsung store within a store located there. Many Best Buys do and these Samsung stores within a store are staffed by Samsung employees. They may be able to help get your J3 back up and running.