Ford Fiesta Door Mirror Not Fitting Properly

[ArabianShark]

Hello.

Recently, backing out of a parking spot, I caught my passenger side door mirror on a pillar and wrenched it rather severely. Nothing broke, but the casing snapped out of place and the mirror assembly was pulled a little ways out of its socket.

Re-assembling the mirror case was no trouble at all, and everything, from the indicator light to the orientation motors, works perfectly, but the mirror isn't properly fitted to the door. The piece of plastic that connects the mirror case to the door panel doesn't lie flat on the door; rather, it's pretty loose.

I found the nut that holds the mirror in place, and managed to undo it (it appears that the bold that holds the mirror wasn't bent), but, when tried to fit the mirror back into place, I found a metal prong next to the fixing bolt that doesn't seem to have anywhere to go, and prevents the mirror from fitting into place properly.

How can I fit my mirror back into its place?