If BTCall cannot find your BT device, please contact support and try this:
Enable BT in phone settings and open BTCall: BT status must be enabled, the Status dialog must report your BT device informations.
Disable BT in phone settings and open BTCall: BT status must be disabled, the Status dialog must tell you to enable the device.
Check if your handset connects automatically on phone calls without BTCall installed, or if BTCall installed, disable all preference settings.