Sue them for environmental damage via their energy contracts and request this information under the Aarhus Convention, which your country is a signatory to.

In case your electricity is run by the government you might also have Freedom of Information laws like Austria, Slovenia or Sweden that would grant you access to such public-sector contracts, if requested.

This is mostly the same here in Finland (one of the cheapest non household electricity prices in Europe.)

Though I don’t see much of an issue as that is just a contract between two private parties. What is the ownership structure like in Iceland?

Also in the case of some of the most electricity consuming industries they are mostly buying from themselves (Pohjolan Voima which is a owned by a group of heavy industry companies)