If your purchase was made through the App Store, you can request a refund through Apple, following the standard procedure for in-app purchases. Contact the Apple Care team for assistance, and find Apple's contact information here.
Please note that purchases conducted via Apple's system are governed by Apple's Terms of Service. As per section 3.3 of our Terms of Service, MasterClass is unable to facilitate refunds or extensions for purchases processed by Apple. For more information on how to request a refund from Apple, please visit their help center article here.