You can’t call anyone unless your billing is through BT. There is no number for TV memberships the phone number is reversed for broadband customers only.
The £10 offer is NOT permanent and when that deal finishes you’ll have went up to full price which just now is £33.99. Also most offers on the website do include a week free trial of boost, then after the week it’s £5 unless cancelled and this is indicated on the website.
To stand any chance of a refund you need to go onto live chat. Which is accessed by clicking “chat online” within the green box. Don’t hit “get help quicker” as this is a bot.
Or email support using the address in the below picture.
FYI that I do not work for NOW, just a NOW customer trying to help