No idea how things work in Switzerland, but here in the States, I'd be involving the Better Business Bureau to tarnish their reputation far and wide, and possibly the state Attorney General to go after their business license, and possibly taking them to civil court seeking restitution.
They charged you 3x the estimate for repairs that did not fix the original complaint, and another dealership pointed directly at the problem in a matter of moments; on top of that, hundreds of shadetree mechanics on MVS read your story and said "yup, driveshafts".
You should have demanded your used parts so you could prove they replaced non-defective parts. If they refuse to give them to you, then (here, anyway), you'd be able to call the police and have them arrested on the spot; the used parts are still your property, and keeping them without your consent is theft.
Jerks like this give the stealerships their bad name. It's probably their fault Volvo couldn't post the profits it needed to.
1997 850 GLT sedan, 152K and WHOOHOO!
RIP 1996 850 wagon, 201K, hit by a runaway 4-wheeler
RIP 1996 850 GLT sedan 5spd, 260K, rearended someone
RIP 1986 245 boring, 200K, rusted beyond inspectability
RIP 1981 242 turbo 5spd, 300K, serious teenage crash