Cellular data limit reached?

A

AC Question

Hi. My internet on my phone has stopped working. I get a notification that says that my cellular data limit has been reached. What does that mean?
My dad said that I have unlimited with data and I've used more before than I have this month.
It also says
"Your device turned of data because it has reached the limit you set."
But I don't recall setting a limit.
Either way can this be fixed?
Any help is appreciated