The VW Commercial dealership in Poole is Breeze.
We bought our Cali from them in 2024.
Although we haven't had any work done by them as we travelled over 200 miles to collect the Cali, they have a good reputation and know Cali's inside out.
The fault isn't California specific but based on the positive feedback I have read, I would be tempted to trust them to do a good job over some of the other VW Commercial dealerships out there.
Id your van still under warranty? If not, perhaps someone may know of a good independent in the area who could probably fix it for lower cost than a main VW dealer.