Don’t sign up for this. I regret it

They debited me for something I didn’t even use and cancelled. Telling me that I was in arrears. How does one become in arrears for a month to month SIM card. From my understanding when I signed up. You don’t pay then the wifi goes off and that was that now they are running this as if it’s a contract. I cancelled on Feb and the WiFi went off immediately now on the 25th of March they debited 2 R499 claiming it’s for 2 months, 2 months now when the wifi was off cause I cancelled