Stop debiting our account!

I manage a small business, and the previous owner and director never changed her Cell C contract payment/debit order details. The debit orders have continued to go off the business account without my authority. The account is in her name, and she has taken out new contracts, renewed others etc. etc. I have tried to request that Cell C stop debiting the business account, but this has fallen on deaf ears as the account is in the previous owner's name, not the company's. I tried to cancel the contracts as they were up for renewal, but again, hit a brick wall (and the account holder renewed them, again, without any authority from the business). How is it that we as the bank account holder have no rights!!!??? This makes absolutely no sense to me.