It would not be from texts unless it is data based texts like imessage or whatsapp.

Are you checking your data usage in your phone or in your prepaid self serve?

I’m using imessage mostly, nothing else and it’s been texts, maybe some links.  It’s not big usage amounts but I’m concerned as the phone get used more.  I’m checking on the portal.

imessage is not SMS (texting).  That is not unlimited.  Imessage uses data/wifi

I have been connected to wifi all this time.

Make sure wifi assist is turned off.

You may want to monitor your data usage via your iphone (Settings > Cellular or Settings > Mobile Data).  You may want to reset your data usage here to get a better understanding what is using data on your device.

https://support.apple.com/en-us/HT201299#:~:text=View%20how%20much%20data%20you,Cellular%20or%20Settings%20%3E%20Mobile%20Data.

Thanks Dennis, I will do this.