It's been a long time since I last experienced your problem with my Nokia 616, I remember I did a factory reset to fix it. I'm quite sure it is a bug in the old Nokia rSAP devices.
The only thing you can do is to reset as much as possible in the car phone. Since there is no factory reset option for the VW Premium (although I remember I once saw one...), at least delete all users. Then switch off the car, lock it and wait for a minute. You may also try to remove the connector from the Premium box below the passenger seat, this also resets additional data, like stored SIM PINs.
If you didn't wipe your phone after switching ROM, at least remove the car from the Bluetooth devices in Android Bluetooth settings.