I'm adding to this thread again with some more information for anyone who comes across it. It's now 2 weeks since my Quickstart installation date, and I've got no connectivity at all. I've made half a dozen calls to customer service, a couple of threads here, and I've had 2 engineer visits in that time.
The issue appears to still be with my account. Your account is much more than just a username and password; it's all the configuration data for your router and your 'place' on the VM wider network. The most recent engineer who visited was excellent, but couldn't do anything as all the hardware and infrastructure is absolutely fine.
What he suspects and has escalated is that when my new account was created as part of the moving house request, someone has basically 'copied and pasted' all my account details from the XGS account to the DOCSIS one. That means the DOCSIS Hub is receiving data that an XGS Hub would expect, and it doesn't know what to do with it. The result is no WAN IP allocation, and dozens and dozens of strange critical failures in the network log.
He said one of the numbered errors is 10998, which is rare or unusual. The escalation is to some internal team who will have to spend some time rebuilding my account, or hopefully deleting it and starting again.
My complaint at this stage is still twofold; firstly that the customer service on the phone is so awful, that any contact with them means they order an engineer which I now realise pauses or cancels any extant tickets, and actually sets you back. This means the 4-5 days I've been waiting for an engineer, no work has been done on fixing my account.
The second issue is that this is all completely opaque; there's no contact from VM about this ticket, there's no confirmation that it's being worked on, or that anyone is handling it; as of the engineer leaving, it's complete silence. If I call to ask, I'll end up with another engineer booked, or the awful CS team deleting a ticket or causing more issues. If I don't call to ask, how long am I meant to sit staring at error codes and hoping that someone fixes it?