Hopefully you purchased some food – AY will cover that if you ask for it. They might want to see receipts.

You would need to proceed to KRIL, and document "SAS Plus" (which KRIL probably has no idea about) for example by taking screenshots from the SK webpage. Now is a good time because SK is about to introduce a business class cabin on Euro routes, so clearly they cannot have it today if they are introducing it "tomorrow". So document what SK Plus actually is, explain this to KRIL in your application and ask for EC261 downgrade compensation. It is a certain percentage of your ticket price, depending on flight length.