You have to sign a separate contract in order to keep your phone bills under control. One option is to set a certain monthly sum that marks your maximum allowed monthly payment, and if necessary, order a notification system to let you know when you have exceeded a certain call limit or data volume limit. Such services include balance notifications and balance stop etc.
If the phone is used by your child, consider ordering the service that restricts calls to premium-rate phone numbers. This way you will avoid calling premium-rate telephone numbers and bills that are unexpectedly large.
In addition to special tariff calls, children may cause huge phone bills by using mobile internet and content services. Talk to your child about these dangers and enquire you mobile network operator about limiting options for various services.
Prior to ordering any aforementioned limiting services, make sure you understand their terms and conditions. Find out how the operator determines the fulfilment of the limit. Your bill may exceed the sum you have set as the limit if it is checked once a day and not in real time.
Determine the cost of the limiting service. Some mobile network operators do not charge for signing up to use a service, but the service might have a monthly fee or charged notifications (e.g. fee for every notification message sent).
Do not mix up a credit limit and the service of keeping your phone bills under control. Since you pay your operator for calls and other services only after using said services, your operator has set a monetary threshold or credit limit, up to which you can use the services of the mobile network operator. The size of the credit limit is set by the operator when the contract is signed.
Be sure to read carefully what your phone service contract says about credit limit. You have to monitor yourself as to not go over the limit. In order to change the size of your credit limit, turn to your operator, whose approval enables you to either increase or decrease the limit.
If you exceed your credit limit, the operator has the right to restrict services provided to you if they deem that necessary, but it is not compulsory.
If something remains unclear about the size of credit limit or the rights and obligations tied to it, ask for additional information on the matter from your operator.
Operators do not monitor going over the credit limit in real time, which is why you may not always receive a notification about exceeding your credit limit and be able to keep using the service. This is especially likely to happen when you make phone calls and use services in foreign countries.