The symptoms, the label, and the german text from the seller all confirm, without any doubt whatsoever, that your nav is coded for a mono screen - also known as the radio-navi.

There is nothing wrong with the unit, it is simply configured for a different display.
It needs to be re-programmed as I mentioned.

To re-program you will need:
NavCoder
OS disk
ibus interface (build one or buy a Resler interface)
laptop
instruction from me

or of course you can pay a dealer to do it for you - although I recall you had a rover, so unsure as to what will happen.