Unauthorized Debit order for payment already made

I cancelled my contract and it was confirmed on 06 May 2015, after I paid the cancellation amount of R3 499.12. I received a statement reflecting that I owe Cell C an amount of R3 498.13. I called customer service and was told that the only amount outstanding was R126, which I paid on 17 June 2015. On 20 June 2015 I received an e-mail from Cebisile Shezi confirming that payments were allocated to my account. It was also confirmed on the telephone conversation that no amount will be debited to my bank account. On 30 June 2015 R3 498.13 went off my bank account. I e-mailed customer service but received no reply. Ref no *** & ***.