You might want to try deleting all devices from the unit. Here are the instructions for a pre 2005 visteon ULF.

Deleting Devices
The paired BluetoothTM mobile phones can only be deleted as a single group
from the ULF control module.
The pairing procedure must first be activated, and then the send/receive
button on the installed eject-box or the pairing button located at the rear of the
center console must again be depressed for an additional 10 seconds after the
“Bluetooth Pairing” message is displayed on the radio in order to clear the list of
paired devices from the control module and the message “paired devices
deleted” is displayed.

I think these are the instructions for a 2005+ BT/Assist module

Isolating
If you no longer wish to use the Bluetooth interface, you can isolate your mobile phone.
This process isolates all mobile phones that have been paired with the interface.

To isolate the paired mobile phones:
1. Press the button above the mobile phone mounting for about one second and at the same time
2. Turn ignition key to position 1
3. Release the button. "BLUETOOTH PAIRING" appears in the display or on the monitor
4. Hold this button pressed for about ten seconds until a triple acoustic signal is emitted.
"PAIRED DEVICES DELETED" appears in the display or on the monitor
5. Turn ignition key to position 0. The mobile phones are now isolated.
The phone book entries that you have transferred from the mobile
phone to your car radio, radio and navigation system or on-board computer
are likewise deleted in the process.

Dennis