Uprofessional service

I had an accident when my new car was 18 days old someone bumped me from behind my car has been with S&E panelbeaters for 2 months for a repair of the damages on the bumper they told me the parts were sent to back office to and fro Today I am going to collect the car which still needs a new part the panelbeaters told me to they're going to put the old part back because they didn't get the correct part from HAVAL Miway took my car to a panelbeater who did mediocre work I am not happy with this I am not told the part will be reordered but why are they using this panelbeater who don't check part when the car was with them for two months