Just want to make sure I understand what you are saying. You were in default and but no longer because loans are now at Navient and you weren't aware so you received a negative remark on credit report?
+1 to everything above.
The status of your student loan(s) is pretty important before we can help you.
Whether or not they're (still) in default is a key piece of info that we need to be sure about.
Also, where are you getting your score from?
+1 What Mookey says - unfortunately, student loans can be finicky and we are just trying to get all of the information we need to help you the best we can.