Hi @mgcmarcel and welcome to the Community! 🙂
Student subscriptions are valid for a 12 month period from the date of signup. This verifcation has to be renewed yearly. My first suggestion would be to see if you received an email from Spotify back in May/June with renewal details - otherwise your account does revert to regular Premium.
You can also read more on the student plan at this FAQ page.
Hope this helps and have an awesome day! 🙂