Instagram using data when data is turned off

hello,

So I turned cellular data off for instagram, but it still loads, which consumes a lot of my data when Wifi is not available. When I'm at work, the WiFi is intermittent and I have to be on Instagram a lot and I’m using instagram without knowing it's not using the Wifi, but it's using my data and I have no way of controlling it.

Anyone knows why this is happening and a solution for this?

Thanks!

Kristin