Your contract only starts on the day it is all installed and activated and then you have 14 days in which to cancel without any penalty charges - so no need to do anything yet, If you do want to cancel it once it has activated - see this old post.
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See the link -
https://www.virginmedia.com/help/leaving
1. if a new customer within the 14 day period - completing the cancellation form you have been given as part of your welcome pack and returning this to them at the address specified on the form (the Sunderland address?).
2. Or call 150 from a VM phone or by dialling 0345 454 1111 - select options 1,1,4,4, - thats the UK based retentions team - but calling at 08.00 is the best time to get through without being diverted offshore I would record the conversation too. "TOP TIP: If you're struggling to get through or are tired of waiting in the queue - you can try Virgin Media's cancellation and retentions department directly on… 020 3743 6947 or 0800 952 2277 or 0800 052 2001 - - or some have used 020 3743 6947 - but no guarantee of getting through on these either though
3. If you wish to give your 30 days’ notice you can do it by just sending a WhatsApp with a description of the cancellation to +447305 327 112
4. Cancel In writing (best way!) to…
Virgin Media
Sunderland
SR43 4AA
Include dates, name ,address and all account details. They say to also include your phone number so they can call you to confirm - probably to make you an offer to stay.\
Do it by registered mail next day delivery guaranteed and with a receipt for signature on arrival.
Whatever you do DO NOT cancel your direct debit until the final bill has been settled or or it will cause all sorts of issues you dont want.