Motor guru centurion sucks

I took my car to motor guru centurion,the white guy Charge me r450 to diagnose my car but said he won’t charge me for diagnose if he fixes it,never knew he was joke he messes up my car without diagnose or fixing and still insisting I pay him.He made a statement saying “You’re a foreigner and there is nothing you can do” please help me hellopeter I need my car back in good shape