Where can I get fixed my Peugeot factory fitted sat nav ?

I have recently bought a 2003 registered Peugeot 406 GTX diesel automatic. The sat nav cd drive accepts the cd perfectly well (new cd bought from Navteq and tested as OK by Peugeot main dealer), the screen, however shows "cd unreadable".
Peugeot main dealer advises replacement, local audio + shop can't help, Halfords etc similar.
Short of hitting the unit with a club hammer, I'm stumped.
Any know who does repairs ?