I used them for my VW Touareg (the van centre is next door to the car garage). A software update took them 2 weeks. Then they forgot to phone me to say it was fixed which it wasn't. Googled the issue when I got home, changed a few settings and hey, all works perfectly. I too was "charged" a diagnostic fee but as the issue was covered under warranty, I didn't have to pay anything. They did however send me an invoice for some reason.
To be honest every time I've dealt with them it's been a nightmare - from picking up a brand new Golf that had a chip in the bonnet which they just touched up to saying I was lying that the rear wiper didn't fit my Tiguan and when they came out to look they had to eat humble pie!
Western for me is a very last resort!
You could try Fife Auto Tech in Glenrothes but not sure if they do warranty work. They sorted my T6.1 suspension for me and are very good.