White-blazes

Hi all, my first post, please excuse me from not posting in introductions section firstly. Our battery went flat in Airport car park before Christmas and the system is now asking for a password. We’ve tried the usual obvious ones and today the car is in the what was Subaru dealer we bought the car from, only they are scratching their heads and can’t solve it. It’s a maroon XV and the previous owner was from Broughton, Chester but isn’t listed in telephone directory. The garage think he may have put his own code in, or even one of the other previous owners (it’s had 3). Really fed up now with no stereo and coming close to changing my blooming car! Any suggestions? Thanks in advance peeps x