I don’t want to subscribe Youtube premium service.
I want to refund the YouTube premium payment. I paid through iTunes, but I want to cancel my YouTube Premium subscription twice and get a refund.
iPhone 6s, iOS 12
To stop its auto-renewal : View, change, or cancel your subscriptions - Apple Support
In terms of a refund purchases are considered final as you know, but you could try the 'report a problem' page to contact iTunes Support and see if they will refund you as a one-off : http://reportaproblem.apple.com
Or you can try contacting iTunes Support via : http://www.apple.com/support/itunes/ww (click on your country's flag, the country where you live, and which is therefore the country on the account ; click on Contact Support towards the top right ; click on Get Help under 'Talk To Us’)