Documents uploading to Sharepoint althoughI didn't set it up

Yesterday I began receiving email updates telling me that the Word documents I was working on have been uploaded to Sharepoint. This happens every time I insert a comment into the file. This only began to happen yesterday.

I have never used Sharepoint, and only learned about the "Share" option when I searched Help to find ways to turn it off. I didn't turn it on deliberately. So I googled for instructions on how to stop this, and none of the instructions I found matched what I saw when I tried to turn it off in either the document or FIle Explorer. 

I just went into Word and clicked Help to identify the version I'm using, but they removed "About Word" from the Help menu, so the version isn't where it belongs anymore. I don't know where they put it, and it might not matter anyway. It's probably the latest version, in fact, this might have happened with a recent upgrade, I don't know.

If my documents upload to Sharepoint, they're private, right? I'm a writer and I don't want my stuff going out there without me controlling things.

Where does Sharepoint keep my files? I no longer have access to OneDrive because I was shut out one day when when my internet carrier switched my signal to another city, and I clicked "No" when Microsoft asked me if I was the one signing in from that city. They immediately locked me out of everything. I can't even get codes by text anymore. I got Outlook and microsoft.com back by signing in with my thumbprint on my phone, but it didn't help me with OneDrive, and I couldn't get support, so I've been unable to access it for months. If Sharepoint is happening on OneDrive, I might be in trouble. 

How do I stop uploading files to Sharepoint, and stop these annoying emails whenever I add a comment to a file? Thanks!