If your purchase was made through the App Store, you can request a refund from Apple just as you would for any in-app purchase by reaching out to the Apple Care team here: 1-800-APL-CARE (800–275–2273) or check here for local numbers.
Please note: Any purchases completed through Apple's system are subject to Apple's Terms of Service, and MasterClass will not be able to process any refunds or extensions for purchase processed by Apple per section 3.3 of our Terms of Service. Apple also provides more detailed information on their Help & Support website.