It’s a tricky situation. I’d be fairly certain that those (or at least one) caliper bolts wasn’t done up correctly. The bolt has come out and all the other issues have followed. So, I‘d also be fairly confident that the workshop that fitted the calipers is the primary culprit.
However, (if I have understood the various posts correctly) it seems that there has been considerable time between the fitting of the calipers and the failure happening - but not a lot of mileage. I think that the extended time will make it a bit more difficult to legally prove the connection between the fitting of the calipers and the breakdown, than if it happened within a week or two.
I think you have to work out want you want to achieve, and then work out how to achieve that aim.
I think you have already been back to the place to discuss it with them and they have (to put it politely) denied any responsibility. This is unfortunate, and makes life more difficult for all concerned.
If I really wanted them to pay and admit fault, I’d be taking the full legal pathway. But I suspect that it will cost a lot of time and money upfront (for engineering reports, etc.). I don’t really know how long small claims and the like take, but I wouldn’t be surprised if you are waiting a year, and even then there would be no certainty as to the outcome. You might win and still be out of pocket.
If I were in that situation, I think I’d probably just get it fixed and move on. And chalk the whole episode up to experience (and not go back to the place that fitted the calipers for any future work). I’d just want to get my car back on the road, and know that the work has been done correctly. I’d be reluctant to have the original place involved in doing the rectification work.
An ‘in between’ option might be to engage a local solicitor to write them a letter of demand (or whatever they call it) and see if they come to the party. They might say ”bring it in and we’ll fix it”. Or they might not. But if it were me, and the original place does fix it, I’d be immediately taking the car to another place for an independent inspection. Or at least I’ll be checking the caliper bolts are tight myself.
One thing that might work in your favour is if they have provided an itemised invoice and it doesn’t show new caliper bolts. Holden explicitly state (multiple times) in their service manual that the bolts must be replaced with new each time they are removed. Yes, I know many people do reuse them, but legally, the workshop isn’t doing the job right (by defying manufacturer’s instructions) if those bolts haven’t been replaced.
In summary, I do think you have a case, and I strongly suspect those bolts were loose, but pragmatically I think I’d save myself the cost, anguish, and delays and just get it fixed properly. And chalk it up to ‘live and learn’.