Double debit on my personal loan

I took out a personal loan with Nedbank which up to now never skipped a payment. my debit date is the 1st of each month, however I have always been paying in advance because my salary date is the 20th and I was never double debited until this month. I transferred R3 000 on the 23rd of August and I was debited R1 800 the same month. I have been calling the call center for days asking foe a refund and I was taken from pillar to post. I spoke to an agent at collection Xolani Mavuso who was rude and not willing to help and go an extra mile to assist. he was not representing the brand and he did not show any customer service. After asking to speak to his tam leader, he came to the line and logged a call for a refund, but never called me back to update me. I had to call the call center again to find out the progress, of which i was told the account its closed and it will be difficult to open the account and give me a refund. I'm by this event because I have been with the bank for over 20 years. This personal loan final payment is for September and not August. The money they double debited is for my rent and as i report this my rent is already due. I was planning to do more business with the bank but at this rate I'm considering to cancel everything with them