If the company has activated a phone line in return for a set amount – for set-up –and it offers a service allowing you to receive calls without paying, and it does not charge anything except the price of outgoing calls, then there is nothing wrong with what you have done, and you do not have to call other people in order for your action to be permissible, because the company has agreed to that and it has taken its due by charging the set-up fee, and it has taken the cost of the incoming calls to your phone from those who call you.
But if the company charges a fee for use of the phone per month in return for activating the line for both incoming and outgoing calls, regardless of whether the line is used for both, then it has the right to be paid these fees, even if the owner of the phone does not make calls and even if he does not receive them, because this fee is in return for a real benefit, and he is the one who is not making use of it. This is like when a car or apartment is rented but the renter does not make use of them until the contract period ends.
Your implementation of the answer is up to you in your country, depending on the system of the company that has activated the phone.
And Allaah knows best.