2013 Octavia - iPhone USB media player not working

Hi all,

I have just purchased a 2013 Octavia with the Amundsen infotainment & satnav system. I previously had a 2015 model as a company car and used an old iPhone 4 as a media player plugged into the USB port under the heating controls. However on this vehicle it doesn't recognise a USB device is connected. I have also tried plugging in an iPhone 7 with a different cable and that isn't recognised either, so I know it isn't the cables. Both phones get power from the port and I have checked the Skoda update portal for updates (there are none available). Any ideas how I can get them to be recognised by the software? Any help would be very appreciated!