If you logged in to the game and found that you no longer had any credits, it's because they have been spent.
Usually, this is because someone else has used these credits (such as a friend or family member). It is also possible that you have played the game on someone else's device and have not logged off. This person could play with the account without you knowing it.
The game cannot spend the credits by itself. Purchases must be requested by the user. Accidental purchases are possible, although we have added a series of intuitive confirmation steps to avoid these situations.
To prevent these situations from occurring in the future, remember to lock your device and log off after playing on a shared computer. Also, if you have loaded the game onto someone else's device, remember to log out after you stop playing.