Delays in Quickstart delivery, but can't contact Virgin to cancel or change delivery date

I ordered Broadband with a new hub yesterday (8th April). When signing up it said the Quickstart installation package would arrive within 5 working days. I got a confirmation email saying my package was on the way and would be delivered on 11th April. I have just had a new email saying they now can't deliver on that day, and the new delivery date is 20th May, 29 working days after order.

I have received my pre-contract information but no welcome email, so have no account number, therefore cannot contact virgin to change my delivery day or cancel. I work from home and would be without internet from 1st May when I move in, which isn't really manageable. Anyone know how I can get an account number and contact virgin about this?