I have app**** for a...

I have app**** for a car which is a 2008 model Nissan np300 which was a R150 000 but they offered me a Isuzu D-max which is R280 000 at first looking at it I thought I was going to afford it but I look at my finances after signing contract and calculating everything at home with my wife I can see that I won't afford the vehicle anymore,I did not collect the vehicle so I went in to tell the and wrote an email but their forcing me to take the vehicle or I will be black listed so I need help from you.