The only country sinking russian war ships is Ukraine. US betrayed and EU won't do much of anything to really help beyond bare min required to save face.
Russia also should really not want to be at war with the EU, but as you noticed, they don't seem to care much about what they should do. If they fuck around enough, they may find out, but they are betting they won't.
For balance, the last time this happened, when people were calling for nukes on Moscow, Sweden investigated, decided it was not deliberate, and released the ship
Place sea mines defending the cables. Post maps for civilian ships to keep out of the mine zones. Anyone goes near the cables anyway? Well, you were warned.