Should I cancel my Paramount+ premium or Apple TV Channel subscription first?

• The subscription with Paramount+ directly is for use with the Paramount+ app, on any supported platform, and even their web access. You would pay the fees to Paramount+ directly.
• The subscription for Paramount+ as Apple TV app Channel is for use with the Apple TV app exclusively, on any of your supported devices, including select third party devices. You would pay fees through Apple from your Apple Account.
• The subscription for Paramount+ as in-app purchase from the Paramount+ app on an Apple device, is for use with your supported Apple devices that have the Paramount+ app. Not web access, not third party devices. You would pay fees through Apple from your Apple Account.

Keep the subscription type that fits your needs best. Cancel the other(s).

To cancel a subscription with Paramount+ directly, go to your account settings on their site.

To cancel a subscription through Apple, go to your subscription settings on any of your Apple devices. If you want to cancel a subscription from Apple - Apple Support

Refunds request approval (or denial) for recent payments through Apple is done on a case-by-case basis. In principle, all sales are final, and you agreed to that. Older payments may not be refundable, as Apple would have already paid the content provider in the mean time after some waiting period. Request a refund for apps or content that you bought from Apple - Apple Support. Apple staff may choose to be lenient on accidental or unintended purchases, that are not repeats.