HERE's an ODIN tutorial on Youmobile. Sorry, if you already know how to use it, but can't tell from the thread.
A few things...
1) Kies cannot be running on the computer or it may mess with ODIN (perhaps the same goes for Smartswitch, but not sure). Be sure neither is running... check Task Manager and End Task if they are.... or uninstall the programs.
2) Be sure to start ODIN before putting the phone in Download Mode and connecting it to the computer
3) Be sure NOT to use a USB hub... connect directly to the computer USB port... preferably in the "back" of the computer (best chance in case the front ports are underpowered)
Basically... turn off the phone or pull the battery, pull the SD card (leave it out), start ODIN, load the firmware, put the battery back in the phone, enter Download mode, connect phone to PC.
Hopefully ODIN will see it.
If your want to try LP 5.1.1, you can get it from
HERE. Use the "Full Firmware" of N910VVRU2BPA1. All you need is this firmware, nothing else.
I'm not an expert with flashing phones, but I've done a few to include my recent spare Note 4, which I downgraded from MM to LP 5.1.1 using the exact firmware in the XDA link.
I hope you can get it going, but if you still can't get ODIN to see the phone, or flash the firmware, then I'm really out of ideas, other than getting Samsung to reflash the phone for you.
Good luck!