iphone docking car stereo

Since I updated my iPhone 4S with the recent IOS update the connection with my car stereo doesn't work. I have bought a new cable and it doesn't work either. As such I can't play music using my steering wheel controls to chnage the volume and move between tracks etc. I have the same problem with my sons iphone so am fairly confident its the software update to blame. I have an old Creative Zen MP3 play which works fine via the USB connection. Anyone else had the same problem and is there a fix?

BTW: I have a Seat Leon, which is part of the VW group, so suspect this may affect other Seat drivers plus VW, Audi and Skoda drivers also.