Yet again Nedbank drops the ball!

For Some unknown reason Nedbank Home loans deducted my bond installment twice this month (even though the account is not in arrears). I call them and the consultant advised me that I must write a letter to them requesting the refund, which I did. It is now almost two weeks later and the refund is still not made. 1) Why must I write a letter to correct their mess? 2) Who authorized them to run another debit order on my account? The more I deal with Nedbank to more I realize they are useless, every second month there is some issue with one of their departments. I need this fixed immediately, otherwise I will take this matter further. Reference/ case number (for my call to Nedbank): ********** 0