The bug has normally been solved shortly after posting.
Do you still have the issue after relogging?
Edit: I found your post in the french news section (please don't crosspost, as you see it doesn't help).
Mario-Pezzella a écrit :
The only way to unlock the situation was to pay with feez for a mission I've already completed. Is there any way to obtain feez wasted for this reason?
You can write a ticket (ingame "contact us" link) and explain what happened and how many fee'z you spent for this bug.