Flights Online booking Website is flawed

I bought a R250 voucher for an excess baggage purchase I did not require. Sure enough they did not allow for cash refunds but rather a voucher worth the value. <br> The purpose of this complaint is to highlight their flawed online booking website. After finding the flight I was interested in (JHB-Durban) I put in the voucher code to see the final price, however I finally decided not to proceed with the transaction, at this point, no names or any other details (payment details) were entered. The following day, I found another flight I was interested in, only to find out that the voucher had been 'used'. <br> This is obviously a glitch in their website. I called yesterday (Sunday afternoon) to allow Mango customer services to rectify the situation, but the truth is that they were not interested in looking after their good willed customers. It is clear they will not receive repeat business from my friends & myself. <br> Their manager on duty (apparently the most senior available) on that Sunday afternoon, could not (or was not willing to) exercise his own authority to re-issue the voucher (or alternatively-supply another voucher) to myself that day so that I could purchase a ticket the same day.