The first thing you need to know is how did you subscribe?
Here are the guides for different platforms that might help.
Apple：App Store subscriptions auto-renew by default, so it is suggested to manually cancel them. You can view your Apple ID in iTunes or the App Store and then select the “Subscriptions” option.
Google：Google Play Store subscriptions may or may not auto-renew depending on many factors. You may check your Google Play Store account > verify if the recurring TickTick subscription is enabled there. If there is, make sure to disable it in case you are charged again.
PayPal: Sign in to your PayPal account and manage your subscription by visiting the URL below: https://www.paypal.com/c2/cgi-bin/webscr?cmd=_manage-paylist