Just keep on billing

I had ended my contract as it had come to an end after 24 months. I went into cradlestone mtn at the end of september to cancel if 20 days prior as that what mtn told me, I had recieved confirmation of the cancellation and yet yesterday mtn took another R509 from my account. Now I need to fight with mtn to get my money back which will not happen. I was on the phone for 3hours yesterday with mtn cutomer care only to be told there is nothing they can do and I must recancel my account and I wont get a refund. Pathetic as no manager would speak to me.