If you subscribed through Apple click on the link for the document 'How to cancel a subscription from Apple' --> https://support.apple.com/HT202039
and make sure you're using the same Apple ID you might have been using when you subscribed. Also read all the details such as having to cancel trials at least 24 hours in advance.
If you subscribed through YouTube itself click on this link: Cancel your YouTube Red membership - Computer - YouTube Help - https://support.google.com/youtube/answer/6308278
For a refund from an Apple subscription, click here --> Request a refund for apps or content that you bought from Apple - Apple Support
For a refund from YouTube itself, you'll have to look that up yourself, sorry.