Voucher not issued for ticket canceled by Mango airline

I had booked a flight ticket from Durban to Lanseria (Jhb) on 25 March 2020 at 20:10pm, the time was changed by Mango on the same day to an earlier time which I responded by email that I would not be able to make an earlier time. A few weeks later I received an email stating that I could change the ticket into a voucher. I have been emailing Mango customer services and mango vouchers numerous times for the voucher since mid June 2020. I still have not received a response and I am reaching a point of frustration. I need to either be refunded my money or get a voucher for the ticket as I need to utilize it asap.

Regards GB Dube email: ***