Start button > left side, click Settings > click Update & Security > left side, click Recovery > under Go Back to Windows 7, click the Get Started button.
That will start reverting your Windows back to Win 7.
After you are back to Win 7, go to Windows Update and set it to Manual.
When there are updates available, read the list. If you see update KB3035583, right click at it > click Hide.
That KB3035583 is the one that will send a Get Windows 10 icon to your system tray.
Hide it and it won't cause any trouble, and Windows Update will not offer Win 10 for download.
So, you will be safe with Win 7.