Read through some of the many 'delayed installation' topics on here and you will get an idea of how VM behaves in this sort of situation.
Start keeping detailed notes on all of VM's failures to install (dates, times, messages emails etc.) to ensure you get paid the correct compensation due for the delay
https://www.virginmedia.com/help/billing-and-payments/automatic-compensation
You can try the pre-installation and delivery team on 0800 052 1734 who are supposed to know what is going on. Most reports on here though suggest they are generally clueless and can do nothing more than read out the date shown on the screen in front of them (without being able to change or influence anything).