Is it possible for any app to connect to Internet over cellular when the data connection button is off? I have the following situation on an Android 5.1 phone.

(I don't think this may be a duplicate as the other similar questions I saw were about intentionally allowing or blocking apps from Cellular access.)

Because of an automatic daily-pass (they call it) charge upon any momentary connection to the Internet, I turned off the Data Connection button (from the drop-down quick menu screen) a little before the current day expired as I usually do to avoid an extra day's charge.

I was also at home next to my always-on WiFi.  This I mention because supposedly WiFi is always preferred over cellular network, right?

Hours after the button was off, I got an SMS telling me that I have connected to the Internet (cellular), and I will be charged for yet another day.  I immediately checked the Data Connection button and it was indeed off as I had left it.

So, I'm curious as to how the connection could have happened.

I want to report the company for fraud.  But, I need to be certain.

Is it possible for any application to override my manually selected Data Connection button position and use the Cellular network for data?  (And, even more so when I'm on WiFi at the moment?  But this is not the main issue.)

Now, if by any chance this is indeed possible, what would be the way to be certain my Cellular data connection is never used until I decide to do so?

Thank you.
After complaining to the phone company, it turns out that the issue is (believe it or not) 4G related.

They refunded my unfairly charged amount, and switched me to a different data plan that excludes this daily-pass automatic connection so this won't happen again.

I have found this answer to another post which is correct for here also.