Request a refund
How do I request a refund for a subscription that was accidentally made on the family sharing plan?
iPhone 7 Plus, iOS 12.0.1
Question marked as
Purchases are considered final but you could try the 'report a problem' site on the account that the purchase was done 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