Hi Mgaud,
If the feature is not working on multiple phones, it is most likely related to an issue with the car system.
There may be an update required to maintain full functionality with newer versions of iOS.
We would recommend contacting the car manufacturer for information on this.
If there is no update available, we would recommend you Reset Network Settings. You can learn how to do so here: Return iPhone settings to their defaults.
If the issue persists further, we would recommend ensuring you have a backup of your data (How to back up your iPhone, iPad, and iPod touch), then Restore your iPhone. You can learn how to do so here: Restore your iPhone, iPad, or iPod to factory settings.
Once complete, Setup As a New Device (do not restore your backup).
If the issue is resolved, go ahead and restore your backup. You can learn how to do so here: Restore your iPhone, iPad, or iPod touch from a backup.
If the issue recurs once your backup is restored, there may be an issue with your user data, in which case we would recommend you sync your content to a service such as iCloud, then erase your device and Setup As a New Device - all synced data will return, though you will need to re-download your apps and adjust your user settings to your preference.
Thanks again!