The chargeable subscription begins naturally on reaching the end of the free trial duration, to give consistent continuous experience. So according to Apple, on the off chance that you would prefer not to keep utilizing, you have to cancel the trial before 24 hours from the first subscription.
The trial is an initial offer and is benefited through AppStore utilizing your Apple Account. A user can avail the trial just a single time. The trial and subscription are managed through Apple.
If you subscribed to the trial through Google Android (through PlayStore), here is the article.