Closed account& Rude Customer Care -Keep deducting debit orders

Just shockingly bad and poor service received from Cell C. I cancelled my contract in April during a visit to the Menlyn branch. I was informed that last debit order will be the end of April. However a Debit order was again deducted end of May. I have emailed and called, but no luck. Today after receiving a statement, and a final attempt to sort this out, the agent hung up on me - shocking!! This nonsense of getting basic security questions wrong such as my name, ID and bank is a delay tactic from Cell C side for not assisting. I am done, trying to sort out this cancelled account out in a civilized manner. It was closed on the 11th of April and according to me I am no longer a Cell C customer. Go and listen to recordings of the account cancellation on this day that was made from your Menlyn Branch. I owe Cell C nothing!