Go into your Amundsen head unit, and "forget" your phone. Immediately after you've removed it, switch off the head unit. Do the same with your phone (forget the head unit), then switch off the phone.
Now, power the head unit on again, browse to its settings, then get ready to FIND DEVICES. Switch your phone on, and setup Bluetooth pairing. When they both 'see' each other, you will be given a 6-digit number on both devices - if they both match, pair them up to each other.
At this point, attach the phone via the USB connector socket in your car, using a compatible cable so that you now create a bridge between the phone and the head unit. You should now have AA working once again.
Okay, that makes sense. Thanks for the answers.