Galaxy S5 :: Exclamation Mark Icon - Background Data Notification?

I set up my phone yesterday and within a short period of time my free 500mb monthly data was gone and then my credit was going down being charged for any more data usage. I would like to figure this out soon or I'll be charged £1 per day for any data I use or use unknowingly.

I would like to restrict background data but when I select 'Restrict background data', within seconds I get a notification saying

"Background data restricted. Touch to remove restriction" ...

And an exclamation mark icon remains at the top left of my screen. Is this normal? Is there a way to clear the notification and the exclamation mark while also keeping 'Restrict background data' on? The only way I can clear the notification and get rid of the exclamation mark at the top of my screen is by tapping on the notification but then background data is no longer restricted. I cannot swipe the notification away and the clear all is not there either.