I got it! See solution below...
How to fix this problem if it comes up:
1) double it home button and kill the messaging app
2) open the messaging app
3) delete the message that says "Unknown"
- do not close the app...
4) after the message thread is deleted, hold the top lock screen button & then slide the button to turn off phone.
5) wait a few min and turn back on..
6) double it home button and kill the messaging app again
7) open messaging app again and boom.... gone!
This was what I was trying to convey above in a comment for you to go your Home Screen and turn off the MSG APP. But you were able to figure the rest - happy days are here again.