ACR is listed in the VM price list
https://www.virginmedia.com/content/dam/virginmedia/dotcom/images/mobile-browse/downloads/010420_Eve...
on page 2 at a nominal £2.70 p.m. for the service. However, the actual cost may well be bundled in with any other services and features you have as part of your VM package so may be hard to identify as an individual cost item.
The code you mention to turn ACR on/off is also mentioned here
https://community.virginmedia.com/t5/Home-Phone/Anonymous-call-rejection/m-p/3918385#M122104
but doesn't appear in the VM phone user guide
https://store.virginmedia.com/content/dam/eSales/Downloads/Phone%20User%20Guide.pdf
so may be a feature specific to whatever particular type of central equipment provides your VM landline service. The same code seems also to be listed for BT equipment in online searches.
Have you tested your new setting is working by dialling in to your landline whilst withholding the number being used to dial in?