Charged for an inactive account

My cellphone network was switched off beginning of September. I did not think anything of it, as I had cancelled the contract. Due to having cancelled it a while ago, I could not remember whether the cancellation was in effect from September or October. Since the phone had no network - I assumed September. But 1 Oct, Cell C took money off my account for this INACTIVE cellphone! Very unimpressed and I want a refund. I will NOT pay for an account which was not available to me!