Singapore Airlines: Unacceptable Customer Service.

I bought return tickets in mid 2022 from Joburg to Auckland for return in April 2023. Booking Ref 6YJHGZ last name Du Plooy. The quoted price was R78k, what went off my bank account was R86k. I have been on numerous calls to Singapore Airlines and no-one could explain the difference, later to ABSA, who indicated that it must be with the Airline, because no international fees could amount to more than 10% of the purchase price. I gave up because there was no help or support from Singapore Airlines. Next Chapter - our circumstances changed and we need to change the return flights from April 2023 to December 2023 - I'm calling the Airline ahead of time you would think, with ample time to fill our seats - we also have one free change of flights as per our booking conditions. Now we are told we cannot change the ticket to more than one year after it has been booked, and we will either forfeit the return tickets or need to pay a cancellation penalty of USD 400 per ticket. I've been flying internationally all my life and have never received such poor customer service. Thanks Singapore Airlines for *****ing us out of R470 on the original booking and now a further USD 1600 - this is big money for a South African. After holding on on international calls to no avail I am not confident that anyone at Singapore Airlines is interested in looking after their customers at all when they are not on the plane itself. I could not even find an email address to send this complaint to! Avoid Singapore Airlines at all costs.