Refund for cancelled flight

I booked a flight that goes to Durban on their website. From the 31st December to the 6th January 2019. I made a mistake and aldo wantef to book a cheaper flight which is Mango. I booked another one because thete was no confirmation that it was booked. I later received the email that says it has been booked. Now i was seated with 2 flight bookings. The correct and the wrong one. I tried to call travel start but failed because their phone kept on playing music. I wrote an email and immediately received an email that confirm the receipt and said someone will call me. And i never received a call. On the 17 or the 18th i tried to call, the 1st and the 2nd receiver put me from a pillar to post. The 3rd receiver of my call cancel the flight for me and i received the email for that. Up until today i did not receive my refund. Im about to travel back from Durban Back to Pretoria but no money in my account. What must one do when things are like this? Make this complain trend on twitter? The money i must get back is R4657. 00. For voucher ZA ********** 2 which was cancelled. HELLO PETER, Can you kindly intervene.