Still being billed for my cancelled account 8 months ago, with little to no contact from Cell C...infuriating!!!

In December I left the country and contacted Cell C to cancel my account. In February they informed me I would have to pay an early cancellation fee and send proof of that payment. That was all done in March. I have been billed every month since then, with repeated emails backwards and forwards to "Nurse" at Retentions instructing him to resolve the issue and refund all this money they are debiting from my account. He keeps passing the buck to "Billings" and refuses to give me a contact person there that i can deal with directly. No one at Cell C is prepared to help me resolve this issue...it is absolutely appalling service, and what about this money being debited off my account every month???