Contract cancellation

I had a data contract with Vodacom. It had expired so I called them in April to cancel. First the girl said I would have to pay a penalty because the contract wasn't over. I told her it was and she said it had been incorrectly marked. She would have to have it changed before it was cancelled. Should be 2 days before she could cancel the contract. I should call back to confirm. I forgot about it but assumed all was fine. Until I got a call that the account was in arrears. Spoke to customer service who said that they couldn't do anything because my account was with debtors. Spoke to debtors and they say they can do nothing about the cancellation, I must speak to customer service. So basically no one can help me until I've paid the account even though the mistake is clearly on Vodacoms side. I've been reading similar complaints on FB and online. Seems to be a common business tactic.