DEBITING UNAUTHORIZED FEES FROM MY ACCOUNT

In May 2020 I cancelled my data contract with Cell C and was instructed to pay a R526 fee to cancel the contract, which I did. I then subsequently emailed the proof of payment to the retentions department. Yesterday, I notice that Cell C debited my account with the cancellation fee AGAIN. Is there a communication problem with Cell C's customers service team and their accounts department?? Why is Cell C debiting my account twice with the cancellation fee when I already paid it in May 2020? After phoning yesterday to log a complaint, the agent arrogantly told me that an investigation will be done but he can't "assure me" that the money will be refunded? If the money is not reversed or refunded to me before the end of this week, I will ask my bank to do it for me and I will also escalate this complaint further and if need be, I will block ALL debit orders from Cell C. This is very bad service!