Assuming you are billed directly by NOW, then if nothing is showing on your NOW online account under both My Membership or My Payments.
Then is it possible you have more than one NOW account?
Check all your playback device NOW App logins for your details.
Also is your bank card details on your account up to date.
There has been a small number of reports that NOW have cancelled some customers NOW TV Membership offers or subscriptions without the customers knowledge.
See if NOW live chat can assist you further.
If you are still going around in circles and can't find your NOW Sports Membership, then jump over to live chat by clicking on the green chat online button box towards the top of this link page below.
Don't click on the get help quicker pop up which is merely an auto bot.
If the transactions on your bank statement say Now or Sky, then you know you are dealing with them direct and not via a third party.
To search for a possible duplicate account the Sports Membership might be on, try this:-
using the card details from the card you know is paying it.