Yes you can cancel within the first 30 days of ordering it as stated in the terms and conditions you sign up to heres a quote:
"We're so confident that you'll be happy with your new ntl service(s), we're offering a money back guarantee. If you're in any way dissatisfied and wish to cancel, you can call customer services within 30 days of installation and request a refund. We'll then credit your account with your first month's rental charges and any installation fees. All we'll charge you for are any calls made, movies, music, any pay-per-view or On Demand events ordered or any service upgrades after installation. 30 day money back guarantee only available to new ntl customers. This does not affect your statutory rights."
So you can give them any reason
