Welcome to the wonderful wacky world of Bluetooth. Delete your car from your phone and reboot the phone. Verify your device is gone from both the hands free calling and Bluetooth Audio (if you have this feature) and turn the car off. Wait 15 minutes to give the car a chance to forget everything and then you can re-pair the phone and car.
Any burp in the system while attempting to connect a bluetooth device can cause this type of behavior. The Bluetooth protocols don't specify what to do when a connection fails for unexpected reasons so many implementations simply drop the connection.
Let us know if obermd's suggestion works out at all. If not, we can look into additional trouble shooting options for you, or connect you with the Infotainment team. We're available via private message if you have any additional questions.