Anybody else in the household have access to any of your playback devices ?
If so, do you have a payment pin on your online NOW account to prevent for example kids accidentally buying a Day Sports Pass directly off their NOW devices they have access too, which can be easily done.
If you go into your online account under Devices see if anybody was watching NOW roughly around the time the Day Pass was purchased by using the time stamp on the email from NOW.
Unfortunately the Device list only see's if somebody has actually watched something on NOW and can't detect somebody browsing the NOW App on their playback devices.
With regards to a refund, get in touch with NOW live chat using the green chat online button from this link page below.