accident, though alrdy fixed and payed but not right

hi, wondering if anyone knows where i stand with this, a guy reversed into me, admitted fault and said i will fix your car.

left car into garage they fixed it, few weeks later paint was coming off it was that thin, phoned the guy and left the car in again

second time into garage fixed and returned, though im still not happy, paint looks a different colour now, very faded and kinda rough looking
not the usual nice shine it was before.

so im not happy at all and dont want to return it to the same garage, the guy is now getting defense as you would be, so where do i stand with getting him to fix it, or another garage and is telling my insurance at this point what happened in or out of the question as i did not declare it from the start. ?

any help advice thanks

mark.