Bad business ethics

Hi I booked two flights with Mango from George to Johannesburg for the 10th May 2021 and from Johannesburg to George for the 22nd May 2021. Due to the uncer*****y of the flights because they were grounded I was advised by them to apply for a voucher. I cancelled my trip and app**** for the voucher on the 29th April it is now the beginning of June and they haven't even bothered to reply to my requests. This to me is a ******** offence there management knew about their situation but they still accepted bookings and took peoples money. I don't care if they are state owned they have no right to keep my money for a service not rendered