@Soph153 wrote:
I’ve tried taking the cover of the wall box off, unscrewing the existing cable and replacing with the new push one but I’m still getting a green flashing light/no connection when plugged in
I’ve also tried plugging the existing cable into the hub with no luck

That is a powered outlet for fibre connections. The cable on the right goes to a plug in power adapter. The connection that goes to the hub is the capped one on the left (see the linked post below). I think these have to be tech fitted if one is not provided in the kit. Your connection won’t work without the wall box power adapter.
https://community.virginmedia.com/t5/QuickStart-set-up-and/missing-power-plug-for-white-box-on-the-w...
VM BB TV Landline. Vonage 2nd line. Freeview/Freesat HD, ASDA/Tesco PAYG Mobile. Customer since 1993
I'm a Very Insightful Person, I'm here to share knowledge, I don't work for Virgin Media. Learn more
Have I helped? Click Mark as Helpful Answer or use Kudos to say thanks