First thing is to check for any “known network faults in your location - Look in 2 places
1) Try the “check service,”Area status webpage (https://www.virginmedia.com/help/service-status)
2) Then also Try the “free & automated” Service Status number - 0800 561 0061 - which usually gives the most up to date info. and tells you of more local issues and fix estimates, down to street cab/ postcode level.
If none reported on both of them, and neither Hub can connect, it suggests that the Hub3 has been removed from your account and the Hub5 added in its place - but has not yet activated onto your account. These often get in an activation queue and can sometimes take hours for it to happen - or sometimes it just hasnt worked at all.
Try a reboot first but then call the equipment activation number on - 0800 953 9500 (follow options) and check with them. You will need the Model numbers, serial numbers/MAC addresses off the barcode stickers of ALL pieces of kit and also your account number