Is what I have done through the internet, in terms of usage and benefit, considered unlawful, based on the principle of "what is built upon falsehood is false," or does my ignorance of the matter permit me to benefit from what I acquired during that period?

You are not at fault for benefiting from the work you accomplished or the money you earned through working on that network, even if the brother distributing the subscription was unauthorized, because you were unaware of his transgression. Sheikh al-Islam Ibn Taymiyyah says: "Whatever ill-gotten wealth exists, or wealth acquired through contracts that do not permit possession, if a Muslim knows of it, he should avoid it... But if its status is unknown, then the unknown is like the non-existent. The basic principle regarding what is in a Muslim's possession is that it is his property if he claims it is his."