The day membership stays on your account for 12+ months. So if you don’t want a refund you can activate it for the next time you intend to use it.
To activate a day membership your best to use your mobile app to kick start the membership. Then switch to the appropriate device.
If you still wish a refund, you’ll need to jump onto live chat and speak with staff. Just make sure you click “chat online” within the green box and not “get help quicker” as this is a bot.