I've recently bought a kit from dillenger, and actually found them to be alright. An email address for them is -
support@dillenger.zendesk.com,
and I'm sure there is numbers on the site you can phone, not that I ever got answered on the uk mobile number shown.
My kit came with a thumb throttle due to them unexpectingly taking into account a conversation I had had with them a few months prior to ordering the kit. I emailed saying I needed the twist throttle as the kit showed and was sent one a few days later, cost free and with no arguments.
Just to check, had you realised the 750w bafang is street legal for the us, not the uk which is 250w? If that bothers you of course
Regarding the rack Kinninvie, have you seen the website someone had set up with regards to replacing the earlier racks? not sure if that wold give you more luck? Hopefully I wont have so much trouble if my kit packs up, but will worry about that if it happens. so far I've found them to be very helpful