Singapore Airlines Terrible Service

I booked a flight from Hanoi to Durban, South Africa with Singapore airlines Booking. On 7 June 2022 I received an email from British Airways saying my flight from Johannesburg (JNB)-Durban (DUR) has been cancelled. I called the Singapore airline international help line (+***) and was told by the agent that they could not help me but they would schedule a call back from the manager on 8 June 2022. I waited the entire day and did not receive any call back. I then had to call back 3 times and ask to speak to the manager Kenshin who apparently wasn't in the office every time. After the third call I was promised he would call me after 30 minutes. After waiting 1 hour and still not receiving a call back from Kenshin I then called the helpline a 4th time and asked to speak to him. While speaking to the manager Kenshin he continuously tried to speak over me and kept interrupting while I was talking. As a manager he handled the situation extremely poorly, At one point he even said that he was going to cancel my flight (without my consent) because I was not accepting the options he was giving me for the flight from JNB-DUR. I chose to fly with Singapore airlines because they were the only airline who included the JNB-DUR connecting flight. I now have to book another flight from JNB to DUR at my own expense because Singapore airlines will not book me on another airline or refund me for that connecting flight. I regret using Singapore airlines. This will be my first and last trip with this Airline. Absolutely disgusting service.