I have just noticed the same problem & didn't receive any notice of the increase for Sports Monthly Pass.
I'm a Talk Talk client who was passed over to Now when they stopped offering Sky Sports.
If their increasing your monthly billing you should legally be informed in writing so you can either accept or cancel your agreement.
Have a read of the TalkTalk NOW FAQ " what happens when my discount runs out" on this link page below.
Because you was on a discounted offer, you need to cancel the offer in the last 30 days to avoid the NOW Sports Monthly Membership going back to it's normal rate of £33.99 per month (unless you cancel).
Sometimes when you cancel closer to the end date of the offer you may get a retention offer to stay.
Or look on the NOW website for any new Sports Membership offers.
Many thanks for your help much appreciated.
Basically after 12 months they Auto Renew with No Reminder.
I wasn't aware of that until now.
I emailed Now & they came back & basically said tough accept or cancel.
Really Not impressed with their Customer Service!