This is one of the anti-consumer things about the Apple App store and it applies to Apple's own apps too..

I subscribed to Apple Music with their 3 month trial and shortly after redeeming, I hit cancel on the subscription to prevent auto-rebill.

It immediately revoked my access to Apple Music and my 90 day trial disappeared. Same with Apple TV trials, etc.

Now I'm forced to set a Calendar reminder when I activate any kind of trial to remind me to cancel before the automatic rebill.