GT Connect Nav+ telephone issues
I've recently acquired a second hand Alfa GT 1.9JTD with the Connect Nav+ system. I installed an O2 SIM card and everything looked fine and was well pleased when I received my first call. However, although I could clearly hear the voice of the caller through the sound system, they could not hear me at all - however loud I talked!!. I've adjusted the volume controls and played with the "mute" button, but nothing I seem to do works. Is there a "mute" button which prevents outgoing sound which I'm not aware of, or do I need to install some sort of external microphone? I've read the Connect Nav+ manual from cover to cover, but can't seem to find any clues. Am I just being a bit thick, or does this sound like a genuine technical issue?
Thanks for anything anyone can provide,