They would most likely write to you. For example, if you have a look through this forum, you will see several topics where customers have received letters regarding malware being detected as operating via VM customers' connections.
You may also very occasionally get a text message from VM if they are doing planned engineering works which will turn off your broadband connection. These texts are for information only and no response is required. These texts don't happen that often in my experience.
VM may also contact you for marketing purposes. If you don't want that, you can opt out by logging in to 'My Virgin Media'.
The scammers are now so prolific, and operate via so many different channels, that the only sensible approach is for you to make outbound contact with VM if you think you need to communicate with them for any reason.