In order to avoid the situation where third parties may use your account, you can disconnect your credit card from your app store when you're not using your device. You can also add funds to your app store through gift cards in the amounts you intend to spend. Please, see information available at https://support.google.com/googleplay/answer/2651410?hl=en for Android and https://support.apple.com/en-us/HT202631 for iOS.
What do I do if someone has stolen my account?
1. Change your Facebook account password.
2. Disconnect all devices from your Facebook account.
3. Contact us and let us know you've gone through the first two steps.
4. Wait until we reply.
5. Reinstall the game and go through the tutorial.
6. Connect the game to your Facebook account in the game Options.