If you mean how to prevent nowtv taking money from your bank card whilst on a nowtv gift card, then either add a new gift card within the last 30 days remaining on the gift card (before the next due payment date) if you want to keep renewing the pass in the future via the gift card method.
Or just cancel the pass, where you will get the full duration of the gift card and add a new gift card when you wish either within the 30 day threshold period or anytime in the future.
Should you cancel the pass, make sure that you follow all the steps on screen until you see the thumbs up cancelled message on screen and next to your pass.
Missed part of your question sorry.
To check if any payments are taken from your nowtv account, go to the NowTV website, then select My Account (sign in with your account details) then go to Bills & Payments where it should show any payments taken.