There needs to be a blockade for these rogue ships. That's the only thing they'll understand, short of being sunk.
Who controls these ships and what is their perspective? I don't understand how we know what they 'understand' or not?
Also, how do you identify the ships? Do you blockade all maritime traffic in the Baltic Sea? All too and from Russia? The first would destroy our own economy, the second is a certain act of war.
Just seize the ships and auction them off. Damaging one cable isn't gonna be worth losing a whole ship, generally speaking.