Poor service from Kulula on refunding flight credits

I have had shockingly poor customer service from Kulula / Comair. After being promised (in writing) an extension on my Kulula flight credits of over R2500, I have been unable to get a response from their team despite multiple emails and phone calls. It has been over a month since I contacted the Kulula Customer Service team, and over 3 weeks since contacting the Customer Relations team. Customer Relations only has an email, no contact number to call, and my emails are simply being ignored.