Mobile data working on gophone plan with no internet included?

A

AC Question

Quick question that hopefully someone can figure out! I have a ZTE Maven and am an AT&T GoPhone customer. I'm currently on the $30 monthly plan which gives you unlimited talk and text, but no data - you can only use the internet if you connect to WiFi. I've just noticed that with my WiFi turned completely off, it's still allowing me to connect to the 4G with the mobile data turned on and use the internet! Why would it be allowing me to do this when there is no data included in my plan? They also can't charge me for simply using data outside of my plan because that's not possible on a prepaid plan.

TIA!