@RP1The Virgin Media Tube WiFi is a complete nightmare to be honest, and it affects all mobile networks, when im in London for work, i don't even try it anymore...
Did you port your number in or migrate from PAYG by any chance?
Have you had a look at the TFL guide at all
https://tfl.gov.uk/campaign/station-wifiAlso above ground isn't always the VM wifi service but provided by TheCloud
If you have I would go back to Customer Services.
- Xperia 1V - o2 and Spusu
- Pixel 8 Pro - o2 and Vodafone UK