Depending on how you are being installed, or whether you are re-contracting services, will depend on when your 14 days cooling off period will start from.
- If you're having a Quickstart install, when the equipment is sent to you to be set up then the 14 days will start from the day after the services have been activated.
- If you're due to have an engineer visit then the 14 days will start from the day they are installed.
- Recontracting? 14 days starts from agreement.
https://www.virginmedia.com/legal
and link from that provides a full set of T&Cs, Section M is what you want labelled "Cooling off rights" (for any contract starting after 27/02/2025):
https://a.storyblok.com/f/253875/x/cdf60bfee9/terms-and-conditions-tv-fibre-phone-from-27-feb-2025.pdf
You can either write a letter in and use recorded delivery, or phone 150 from VM landline or local call from another network on 0345 354 1111. There is a chat function, but historic evidence on this forum says it's about as good as a chocolate fire guard.
If your contract does not have any form of digital signing or request to sign paperwork to return, then its an implied contract and continues unless you notify a cancellation of agreement within the 14 days. If its "pre-contract" labelled, then that suggests some sort of final confirmation would be sent, or a request in it to click something to confirm you are happy to proceed to acceptance. If you had accepted an online offer or one from email, this could take up to 14 days to fully process.