Deducting even though i canceled my plan with them

Hy. I canceled my rain sim R250 off peak plan last month on the 2nd of the month mind you i haven't even used more than a gb and on your page they said they'll will only charge me for the amount I've used so they just deducted R250 from account i don't understand why,i need a refund of my money as i ddnt use a lot of data it wasn't even 1gb nd i canceled so i don't know why I'm paying such an amount