Hope you don't mind our reply in English. Welcome to the Community. We're happy to help you out :)
Since the Student Discount is only valid for 12 months, it seems yours is now expired. Spotify sent you an email to notify that your discount was about to end in a few days. Click on the link provided in that email that says "Extend Discount".
It will ask you to verify your payment method and what school you're attending. After that, it will confirm that your discount has been renewed. If you have already paid $9.99 for this month, just go to this page and re-active the discount and it will start billing $4.99 for the next month.