Can't use mobile data when turning off wifi manually?

[Android Central Question]

I have a Samsung Note 5. I want to use my mobile data to use the internet when in a wifi zone. When i'm connected to wifi, i turn it off manually, but my data also turns off. It doesn't let me use my data when i turn my wifi off manually. But if i'm connected, and i leave the wifi zone and the wifi is unavailable, i can use my data.