loose shower head

Hello I'm trying to fix a loose shower head holder that won't take the weight of the shower head any more. There is no screw to tighten so I assume I have to take it off the rail to fix it. The problem is that I can't unscrew the brackets holding the pole to the wall. Where there should be...

The bracket holding the shower head has come loose, although the screws fixed into the bracket are tight - how can i make the bracket secure so the shower head doesn't keep dropping down?