Unable to reach customer service resulting in losing my flight and extra cost to book new flight

I had a terrible experience that resulted in me losing a flight and incurring extra costs having to purchase a new flight ticket. I originally booked my flight via Kulula in October 2021 and I tried changing my flight on BA’s website and the mobile app. The websites and app did not give me an option to change my flight online and prompted me to contact the call centre. I tried calling all the different phone numbers I could find to speak to an agent. I did get an answer on any of my attempts on numbers ***, ***, ***, or ***. I was waiting more than an hour on ***with no answer even though the automatic response said the average waiting time was 15 minutes. As a last resort, I tried the option of requesting a voucher but also received an email that it is not possible since the ticket was purchased via Kulula and not directly from BA. I then emailed my complaint to *** (the email address provided on the BA website for South Africa), and this also bounced back as an email address that can't be found. I expect to be refunded my ticket or a voucher to compensate for being unable to reach a BA agent having tried ALL the methods as per the instructions on their website as well as the Kulula website.