Hi Coralie
If you haven’t curbed the wheels then the corrosion is nothing to do with anything you have done. Even if they were curbed you wouldn’t lose any of your GCB.
The quality of the lacquer on modern wheels is dismal. A winter with a lot of salt on the roads is often all that’s required to allow white worm to appear on the wheels.
Personally, I would go back to the dealer, if your wheels are undamaged, and ask them to sort this under the warranty.