Apple please send me cancellation letter

This is primarily a user-to-user support forum; other Apple users like you.

There is an Apple article that explains how to cancel subscriptions. Click on the following link: If you want to cancel a subscription from Apple - Apple Support

or use an internet browser to cancel as described in How to cancel Apple TV+ - Apple Support

or cancel in the Apple TV app as described in Manage subscriptions in the Apple TV app - Apple Support

Also, subscriptions aren't usually refundable but you can try the following: Request a refund for apps or content that you bought from Apple - Apple Support