You are legally entitled to unsubscribe from any contract in any way that is most comfortable to you. [0]
For example, you can:
* send them a letter
* send them an email
* call them and tell anyone who picks up the phone
* write it on a napkin and hand it to an employee
All are equally legit and legally binding.
Companies obviously do not want to deal with the manual overhead, so services typically have an easily accessible button for you to click.
Furthermore, companies are required to notify you at least 1 month before any contract is extended and offer you an easy way to cancel - and if they don't you can cancel at any point and get refunded. [1]
[0] for example in Finland: https://www.kkv.fi/sv/information-och-anvisningar/kop-forsal...
[1] for example in Sweden: https://www.riksdagen.se/sv/dokument-lagar/dokument/svensk-f...
EDIT: Just realised Finland isn't Scandinavian, but oh well :)