I've just come off a 1:17 call to tech support. In the end after speaking with a lovely rep, who was clearly not having a great time from clients about this problem, eventually managed to reset my devices.
It worked! I'm on Firefox
To be clear, this problem IS FIXED, but NOT for those who have already run out of device slots.
Please try to be patient with the reps! The lady who helped me had to try quite a few times to reset my devices.
You had more luck than me with technical support. I was advised to uninstall the Windows 10 app and reinstall it - 2 days after it was discontinued ! She could not be convinced it was redundant and declined to offer any further assistance other than to suggest getting my laptop serviced!
The fact remains that there must be thousands, including me, locked out of TV GO through no fault of their own and Virgin Media are taking no steps to find out who has been affected by a problem of their creation and which they have been aware of for ages, let alone apologise, offer a refund or see the service is restored.