Specific for Samsung Galaxy S9 but will likely work for android in General, just different terminology:
After ensuring your USB cable actually works, and your Android Auto and USB settings are still enabled via your car settings then, on your phone go to:
1. Settings > Software Information
2. Tap Build Number seven times > phone will enable developer mode.
3. Exit Build Number > Exit Software Information
4. Select Developer Options
5. Scroll to Networking options, select Default USB Configuration
6. Toggle transferring files to on (what I'm about to say may not be necessary but I'm sharing as it was a part of my process - I actually toggled charging only, then toggled transferring files, following that I restarted the phone).
7. Check Android Auto is working on your car screen, then turn developer mode back off in the settings.