As a point of fact, they cannot, because their goal with "controlling their service" is to control what is displayed on someone else's personal property as a condition of listening to the free data stream they decided to emit.. and so Spotify (or anyone else) is not capable of making that a reality.
They could change their service to try to block users who protect their personal property from having certain harmful pieces of information (like ads) mixed in with otherwise freely available data sources. But it would just be a silly failure, since lots of people already circumvent that type of thing easily and legally with technology all the time.
The only thing they could actually do is to entirely shut down their emitted free stream of data all together, both content and ads alike. Of course they are free to do that if they want. Nobody suggested they have to emit a free stream of data.. only that if they choose to then people will just keep consuming it without allowing ads to appear, and the ads will keep being legally and successfully blocked regardless of any type of ban that Spotify tries to implement.
