I believe they want you to use the API subscription if you want to use their service with OpenCode. It's possible, just more expensive.
That's why we are supposed to have legislation to regulate that utilities and common carriers can't behave that way.
Internet + shitty "security" software that only runs on their hardware + modem rental is cheaper than internet only + bring your own equipment. You can't buy the cheaper internet+security package without their hardware (or so they claimed).