Subscriptions will automatically renew at the end of the acquired period, and you will be charged by App Store/Play Store unless you cancel it. To avoid being charged for the renovation fee, make sure you cancel your subscription at least 24 hours before the renewal date.

To cancel your subscription, please go through the following steps:

Android:
  1. Launch Google Play Store on your device;
  2. Tap Menu, then Subscriptions;
  3. Tap the Color By Number subscription;
  4. In Color by Number's page, tap Cancel Subscription and once again in the confirmation box.
Read more about how to cancel your subscription here: https://support.google.com/googleplay/answer/7018481?hl=en&ref_topic=1689236

iOS:
  1. Access Settings in your device;
  2. Scroll down and tap "iTunes & App Store";
  3. Tap your Apple ID (your e-mail), then tap "View Apple ID" and enter your password;
  4. Now, tap on Subscriptions and select Color By Number;
  5. Tap on Cancel Subscription in the bottom and that's it!

For more information, click here: https://support.apple.com/en-us/HT202039.

If you don't see the options mentioned in the instructions above, please ensure you are logged in with the same Apple ID/Google Account being charged for the subscription. Please contact Apple or Google support for further assistance.