Shortfall Payment arrangement

I bought a BMW 320d 2019 model this year March, I am selling the car back to the dealership and I was informed that they can buy it from me at R 600 000 and my settlement with Wesbank it’s R840 000 I have been calling wesbank trying to reach an agreement on the shortfall amount and I am being told that the only option is for me to pay the shortfall in cash. I don’t believe that I am the only one in South Africa who has sold her car and has a shortfall that can’t pay immediately but willing to get an agreement on the payments.