Hi Katz,
I've got a Calais V 2009 purchased near new (demo). I've had similar problems over the years and it eventually beat me into submission. Holden had absolutely no idea (two different dealerships). Every time I mentioned it in passing they said they'll try a new BT module - but that's not the problem as I also did it myself and it made no difference. Exactly the same as you, can connect, can answer, other people can hear you - you cannot hear them. Holden also checked microphone, and no problem. They sought of 'gave up' in the end...
This is an issue that has both frustrated me, and one that I have researched over many years - and I'm yet to find an answer. People will try to 'flash' the BT version, replace the module (which sits behind the glove box), replace the microphone etc etc. My BT 'looks ' like it's working fine, but doesn't. Holden also stated it could be a 'phone' issue (BT version in car module vs OS/BT version that Apple et al. runs etc). There are many different hypotheses out there. Then, of course, others state their BT runs just fine and with different phones over quite a number of years - so go figure. It really is a lucky dip. I 'think' the series 2 (iLink?) system was better, but then I find others having problems there too.
In the end, I'm going to replace it with a new head unit/setup so I can take advantage of CarPlay/multiple concurrent BT connections and just write it off as a bad dream. It's a pity because when it did originally work it worked very, very well - but that was a long time ago.
That said, if you (or anyone else) finds a fix,
let me know!
Cheers,