Fly safair - NON-SWEETENED deal

I was originally booked to fly before the covid problems - I got a full refund voucher which was great - and then I was promissed a further "20% discount to sweeten the deal". This weekend I rebooked my flight and the actual vouchers worked fine - however, the 20% was not taken off. I was struggling to do the booking and phoned their customer care line and spent nearly 10 mins on the phone with them at my expense. The person who "helped me" on the line told me the vouchers needed to be entered at the end - on the last step. At no point was I told to enter the "promotion voucher" on the first page. (Even though I asked how it needed to be done).

On top of that I repeatedly tried to reach them via their Whatsapp line and that took about 3 hours before they rep****. They then told me that they were "unable to help me sort out the extra 20% as I had already paid the flight immediately". End of story. No help. No further offer to explain. No 20% voucher to make up for the confusion and problems and inaccurate information given by their consultant.