We are paying a monthly fee to a large corporation, in order to gain internet access, in order to generate and exchange Bitcoins.
How is this considered decentralized?
It's decentralized because everyone is paying to different companies, in different nations, and with different goals, associations, and objectives. A centralized system is something like PayPal - if that company were shut down, PayPal is dead. Tell me which company, organization, person, or even nation could be shut down to stop Bitcoin? I suppose it's susceptible to a nuclear holocaust, but if that happens we have more important things with which to concern ourselves. Like the zombies, etc.