correct. most garages will shy away from unknowns , plus the extra training for evs and not a lot of courses. why risk potential damage to the vehicle doing something your not trained for.Just to say also, my guess is the reason many won't work on electric vehicles is because they require specialist training, and they can be dangerous to work on if you haven't had training, and they could also do a lot of expensive damage to the vehicle.
At the end of the day, complex procedures such as servicing a car are not suited to e-mail correspondence, it's not the way garages work. Unfortunately, you are going to have to adapt how you communicate to the way garages communicate best. This means having an initial phone call to get a rough idea if they can help you or not, and then leaving the vehicle with them for them to assess it. You could ask them to inspect first and then quote, I think most would do this. Re choosing the right garage, then you need to make the assessment whether to take to a local or the dealership, and it's here where asking for advice and recommendations will help you - and you can do this on the computer via forums!! Obviously you can ask on our own motors subforum and a lot of car brands have enthusiast forums as well.
I can understand why someone might be interested in a warranty, but my experience has always been there is too much fine print and the insurance company gets out of it, so I would rather take the chance with repair bills.
I am sure that Nissan UK would not be happy to hear about your customer experience, but if you communicate with them via their preferred methods I think you will get better results.
as regards emails again if the garage is a independent they may not have the staff to reply or even read emails, i know when i left the trade they were starting to come in with so called garage packages (web site email even computers. i had one at the unit for 2 years and the only use it got was printing invoices) maybe the email is there but they dont access it.
also to the op im sure i have seen a guy who travels around the country just servicing evs mobile, maybe more expensive but at least he is trained (probably better than some of the dealers who i guess would still put trainees on the basic stripdown with maybe a tech overseeing the rebuild.)