This could be a case of how your billing dates fall. On the basis that you could potentially cancel your cancellation until a day or so before your termination date, VM will continue to issue bills as normal, until your 30days notice actually expires and you're disconnected. You'll then get a final bill with appropriate credits shown.
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
Thanks for posting on the Community Forums, I'm sorry to hear that there's been some confusion surrounding your disconnection request.
As japitts has advised, this just could be how your billing cycle is - you will be billed as normal up until your disconnection date. Any amounts you've overpaid will then be credited back to you in your final bill, which is usually produced around 14 days after your services are disconnected.
You should be able to see if your disconnection order has been placed on your account from your My Virgin Media account/app. Can you please sign in and take a look for us? If the order isn't showing just let us know and we can help further