User field imported with Feeds but not showing in user edit page?
I can't delete foo and recreate it for it contains several data


Here is how I would try to fix this:


Backup your entire Drupal Database. 
With phpmyadmin or some other database manager/viewer, find the field_foo table and extract the table as a CSV file.
In Drupal, go to user manage fields and Delete field foo
Flush the cache (not necessary, but eh, just in case)
Add a new field, foo
Edit user 1 and put something for field foo. (This is just so we get the table structure on step 7)
Find field_foo in DB and extract. 
Open Original field foo .csv in excel and highlight all data and copy. 
Open new field foo .csv and paste data and save
Import new field foo .csv to DB. 
Flush/Clear the Cache
Try importing with feeds again and see what happens.