Is the automatic increase in internet hours balance, without the subscriber's knowledge, forbidden or permissible?

You must adhere to the number of hours for which you have paid, for Allah, the Almighty, says: "O you who have believed, fulfill [all] contracts." If the error in calculating the hours is due to your device, you must fix it; otherwise, you must inform the network owner. It is not permissible to use more hours than agreed upon.