What is the ruling on money acquired from mobile lines, open for international and other use, for which the subscription was 35 pounds per month for 100 minutes, but it later became clear that they were absolutely open for use, leading to a monthly income of approximately 1000 pounds?

"The contract is the law between the contracting parties." You mentioned that the contract between you and the company's agent stipulates a monthly subscription of 35 pounds for 100 minutes. Therefore, you are not permitted to exceed that, even if the lines are open, because that would be an error that does not legitimize your consumption of people's wealth unjustly. You must return to the company's agent, inform him that the lines are open, that you have used more than your right, and that you wish to pay the value of the extra service you have consumed.