Warranty or not, if I handed my phone to a shop to fix and they gave it back to me bricked, I'd raise bloody heck in a handbasket. There is plenty they can do about it including but not limited to a.)fix it or b.) replace it on their nickel. The problem is they couldn't pass this back to Samsung so they didn't want to take responsibility. I'd be seriously annoyed.
Now, that said, if you want to try and restore it yourself, you should be able to do it with Samsung's
Smart Switch
Reinstall or find original firmware with SmartSwitch
1. You will need your phone's Model number and Serial Number
(Both of these can be found under your battery or on the original box -- hope you kept it.)
2. Connect to SmartSwitch in DOWNLOAD MODE and go to MORE > Emergency Software Recovery and Initialization.
3. Put in your phone Name and Serial number.
4. If SmartSwitch will initialize your phone, accept.
5. SmartSwitch will now install the correct firmware for your phone.
Alternately you can try flashing it directly with Odin.
You can download the firmware at
https://www.sammobile.com/firmwares/database/SM-G935V/ and instructions will be on the download page.
Smart Switch would be the better option because it is Samsung's own tool and it isn't a throttled connection like Sammobile.