Bad Customer Service from Mango Airlines

I urgently needed to change a flight booking on the 19th September from JNB to CPT but due to a system issue, was unable to proceed with the changes. The change in fare would have worked out to about R650 if I'd been able to make the changes. All available seats were rapidly disappearing off the system as I was trying to get this resolved. I ended up being forced to book a flight on another airline for a day earlier which came to about R1600. When I eventually managed to rebook the return leg for some time in the future, there was also the added expense of the admin fee for rebooking. I took this up with *** but there was no acknowledgement from their side for the additional costs that were incurred as a result of the system error despite me providing proof of the error message.