Galaxy S7 keeps auto restarting it self even after factor reset

Phone was purchased through ATT US, through contract. Contract is now over.  Samsung Galaxy S7 - standard ATT phone.
I am in New York. Phone is beautiful physical condition.

-- S7 keeps restarting itself and ends up heating it up too much.
-- I booted in safe mode. Uninstalled dozens of apps, ran anti virus scan, no issue found. Freed up memory, about 5.3 GB free on phone.
-- Removed sim card and memory card. Backed up data using samsung smart switch to my PC. Phone did not reboot for quite some time. Felt like it was resolved, and phone did not heat up. But again, after few hours,it started booting itself in loop.
-- I cleared/wiped off cache from boot loader menu.
-- It fails to boot using boot loader, and I see error, "command not found"
-- I finally formatted phone from boot menu - did the factor reset.
-- Phone boots from scratch, and by the time I try to put my google account info in there - it is again in boot loop. It keeps doing this.
-- Is there any emergency software that I can install through PC (Smart Switch)? How will I do it phone keeps rebooting itself?

Let me explain how loyal our family is: we are on ATT since 8 years now! My mother went to Mint mobile, thanks to heavy bills and sub-par service of ATT. T Mobile is offering us free phone, still we won't switch to other, as we are loyal to ATT. Please dont tell me to go for next plan, it is as expensive as buying a new phone. I am open for replacement or discounted new S8/S9 phone.

Help:I need your help in this
1) Please send me clear instruction on how to fix this phone. Including code. I can send you IMEI number.
2) Please inform your NY local store to help me fix the phone without charging fees. That's the least you can do. I can ship it to you, but you can't charge me more money on this!