Sorry that the permissions change didn't do it for you.
For my further education could you check that download folder now & see if the permissions have returned to default?
If it did, that would be a remarkable effort by Microsoft to totally control your pc.
If not, it would mean Microsoft is using a new method to do updates.
I have been update free now for 3 weeks. I did the folder permissions change but within a few days of that I also did the following Task Scheduler changes and maybe that is doing the trick.
Under Control Panel, Administrative Tools, Task Scheduler, then Microsoft, then Windows you'll see 2 tabs - Update Orchestrator and Windows Update.
Disable EVERYTHING inside of both. There will be a minimum of 4 items in each to disable.
Then check your programs and if you have anything like Windows Update Assistant, uninstall it.