What SAT system? ....
If it's not the OE Audi SAT, but uses a FM modulated signal inserted in to the HU via the FM antenna, where you need to tune FM to a frequency like 89.1mhz, to listen to SAT, then the FM modulation adapter used, must be interfering with normal FM signal strength.
The HU won't scan FM stations that the signal strength level is below some arbitrary value, therefore, the failure to stop at any FM stations at all, means the signal strength for all FM stations is below the signal strength needed to stop on a station.
Take the install back to the shop and complain.