Hi there @Pietra_42768 and welcome to 3Community.
As you topped up by €15 are you on 3 Prepay 15? If you are this plan only gives you 1GB of data, if you use your phone to browse social media, or stream films and music 1GB would get used quickly. Have you had a chance to check your usage and allowances in your My3 account? If this is new to you once you've logged in just click on My3 Account and select Allowances or Detailed Usage.
If you're on a different plan please let me know I'm happy to look into this for you.
