Double billed for flight change that wasn't changed

I booked a flight back in June for 18 August and due to change in my schedule I needed to change the flight to an evening flight on the same day. On the 5th of August I went on Kulula website to make the change and followed the process until the website failed with "Application server error" during the payment step. I tried again and received the same message. A few minutes later I get 2 SMSs from my bank with transactions from Kulula debiting me for the flight change. I went back to check if my flight was changed and it wasn't.

I called in and spoke with a Anda Lawana whom I sent all the proof she needed and said she'll look into the issue and call me back. She did not. I sent an email next day to ask for feedback and she said she's waiting on another dept and will process the flight change soon. That was the last I heard from her and it's been 7 days now and my flight has not been changed. Whatever support center you think you have running there is seriously ridiculous, a futile exercise. I spoke to about five different reps and all have zero clue what to do.

I want my full refund at this point. Stay away from Kulula and save yourself a headache.