i didn't "Push the second button from the left two times, then shake the device" as you said, but i'm ignoring your sarcasm now and looking for a solution to my case
"removed the back cover and unplugged the battery"???!!! :confused: how did you do that?
Anyway try the below
http://recomhub.com/blog/how-to-repair-samsung-galaxy-note-5-imei-number-issue/