It wasn't intended to be patronising in any way, so if you've interpreted in that manner, that's an issue for yourself to address.
I am as much in the dark with 'Self-install' as you are, so I spent a little time trying to see if there was anything in our (BT's) systems that may help. I could only find the 'Cut & Paste' that I posted up on the thread, Also, having worked for BT for nearly 30yrs, and the level of incompetence that usually arises through poor training, I suggested that 'Confusion' may be the reason behind the fact the order couldn't be progressed.
I'm basically 'on your side', but you appear to see it as otherwise ?.
I don't quite follow the example you give about one of your neighbours ?? 'Self-install' is apparently only available on Infinity 1 products, and your neighbour is on Infinity 2. The installation also went without a hitch ......... fantastic, but I don't know the point you are trying to make ??
You want to self-install, your neighbour paid for a managed install ......... two different animals.