Flight change without my knowledge or consent

I had a flight booked with Kulula on 10 Dec 2020 at 18:20 and the morning of 5 Dec I just got an SMS stating my flight has been moved to 13:40 on 10 Dec. I tried phoning the call centre to change my flight, but to no avail! And the booking can’t even be refunded form me to book with another airline for the sam time! This is unacceptable! How I am supposed to take another day off work in the current circumstances, where most people don’t have leave to spare?!?!?! The best part of all is that there is a BA flight available for the same time, but they refuse to change my booking that they cancelled to that flight!