Well, I suggest you bite the bullet and reinstall the firmware. In your situation you can use Emergency software recovery in Samsung Smart Switch. This is specifically for Samsungs and made by Samsung, it's not some kids playing with coding so you can have the confidence in know its use will not brick your phone. It will also keep your data intact.
Samsung talked me through that process. In fact the tech took control of the phone and did everything. after 2 hours we finished and it didn't fix it. Sending it to Samsung as they think this isn't and app or software issue at this point.