Vox not refunding double payments.

I app**** for fibre in October with debit order going off monthly on the 1st. Installation and activation was completed on 31 Oct. The debit order did not go off on the 1 Nov. On 2 Nov I received an invoice & statement with amount due on 5 Nov of R804.77 by EFT or debit order. On 5 Nov I noticed that the debit order did not go off. Not wanting my account to be suspended I made an eft payment of R804.77 and emailed the proof of payment. I received an email back confirming receipt and allocation to my account of the payment. On 6 Nov my bank account was debited with another R804.77. I contacted vox and requested a refund. Vox did not reply, I emailed again on 7 Nov, no reply. My account shows I have a credit of R804.77 which vox is refusing to refund or even reply to me. This is not acceptable. I will now lay a complaint with the NCC as vox is just ignoring me.