Google Drive

Hello everyone,
I hope I am in the right place to ask a question about using Google Drive.
I often get an email message telling me that I have almost used up the free 20 GB available to me, yet I intentionally did not put any files there. So, I proceed to delete them, but after a few weeks the situation repeats itself.
I've checked in the settings on the Google Drive website, but I can't find anything to clarify why files from my computer, phone or tablet end up in Drive.
What can I do to stop this obviously automatic uploading of my files?
What and where should I check?
Thank you
Regards
Massimo