If you have purchased the verified track of a course on the mobile app, the steps to receive a refund will be different that regular online purchases and will depend on the mobile platform.
iOS
To request a refund for an Apple Appstore upgrade made on the iOS app, follow the instructions here: Request a refund for apps or content that you bought from Apple - Apple Support
Android
To request a refund for purchases made through the Google Play store, contact edX support by clicking the Help button below or write to billing@edx.org, and request a refund for your mobile purchase. Please provide the email address associated with your Google Play account.