Processes in Microsoft 365 Insider for installing preview builds, activating subscriptions, and keeping apps up to date with the latest Insider features.
What version and build is shown on the File > Account > About Word (or equivalent) menu? When you do a manual uninstall - be sure to follow all steps outlined in the link above, including removing the scheduled tasks, registry entries, and do a full machine restart after completing the procedure - and reinstall Office, what is the version and build that is shown?
The above methods are the only ways to be removed from the program, so we will need additional information if they don't seem to be working for you.
-Jesse