Can't turn off Wi-Fi assist

When I was digging through some setting I noticed that I can't turn off Wi-Fi Assist in Mobile Data. It's grayed out i can't click on it or interact with it in any way.

Things I've done to try and fix this: Reset my Network settings, Updated to the newest version of IOS, Factory reset my Iphone ( I backed it up beforehand ).

This is rather annoying and with my Operator texting me that I've been charged for connecting to the internet ( I don't have data ) it's extra annoying and wasting my money ( or so I believe that this is the cause for me being charged ).

I thank anyone for answering.

Mark