Debiting after cancellation

I have cancelled my contract twice and have been debited after both times. I was or still am on a month-to-month basis. The first excuse was that I cancelled two late and they took a premium of just over R900. The second time I cancelled I did it when they told me to cancel and was debited again a full premium this month. The reason I cancelled was because I simply can't afford it. I explained this boldly when I was asked what the reason was. I feel ****** and out of pocket!!!!