Bitdefender Destroyed Windows Defender

Uninstalled BitDefender Internet Security 2016. Even tried the uninstaller/cleaner tools from the official website: http://www.bitdefender.com/site/view/uninstall_consumer_paid.html . Still nothing. Basically the consequence of uninstalling Bitdefnder has completely borked Windows Defender because now I can't activate Windows Defender. I've tried fixing it per these instructions:

http://answers.microsoft.com/en-us/windows/forum/windows8_1-winapps/error-577-when-i-attempt-to-turn-on-windows/4bf7ef42-7a50-4fe3-88ce-9f13cc2ab0f5?auth=1

But it still doesn't work. I get errors when trying to modify the binary in the regkey anyway: "Cannot edit DisableAntiSpyware. Error writing the value's new contents".

Does anyone know how to actually undo the changes Bitdefender does to your system because so far their tools don't help at all?

OS: Windows 10 64bit Pro.