You can apply for social assistance from KELA if you’re covered by the Finnish social security system and have not managed to find work or relevant studies for the summer.
You will need to describe your situation in a way that makes sense to the benefits officer who may not be familiar with the particular issues you are facing.
Even after that you can resort to the social services of your municipality to help you out.
If you live in Helsinki: https://www.hel.fi/helsinki/en/socia-health/income/income-support/
Also Ohjaamo Helsinki in Kamppi (Fredrikinkatu 48) helps 15–29-year-olds to find solutions in tricky circumstances.
Specialist (social policy)
+358 50 543 9608