App Error and Bad Service

I was loading units for electricity for an amount of R1600. I received an error saying that the transaction was unsuccessful. Naturally because I need units I then processed the transaction again. I did get a message to confirm that I had tried the transaction within 30 minutes and was asked if I wanted to proceed... I selected yes, because the first transaction said unsuccessful. After processing the transaction for the second time and the transaction being successful, I noticed that I was then R3200 less rather than R1600. To top it all to show that there was an error on FNB's side, I never received the 16 digit pin for units when the transaction was unsuccessful. I called in and to avoid saying unnecessary things, was not happy with the service and lack of attempt to help. I don't want feedback that I shouldn't have run the transaction twice and I don't want the units for the first attempt that was unsuccessful. I want R1600 back for the fact that the app said that the transaction was unsuccessful. I was told to log a complaint online and that I would be contacted within 48 hours which is yet to happen. I have gone into the negative now and will now incur additional charges because of an error FNB needs to own up to. Please can this be corrected with my money being returned soonest. Thanks