Ackermans credit account

I have a clothing account since last year and I had a R55 phone insurance and a R65 personal accident cover my total was R680. I canceled the phone and personal accident insurance in the beginning of July even today they still charging me the same installments, when I contacted them a lady said that this is still my interest charged. So basically they charge interest on a month to month insurances and this is not stipulated anywhere in their documents. How am I still paying for policies I've canceled months after I canceled. To me that's day light *******. So disgusting.