Bad service and my vehicle is damaged after repairs at Renew it

On the 25th of August 2017 we were in an accident. Our vehicle was taken to Renew it Edenvale. Authorisation was given on the 1st of September for the repairs. We were told that we would have our vehicle back after 3 weeks. We contacted them on the 25th and they said we will have our vehicle this week. When we contacted this morning they said they are putting an addition in for a part that was never ordered. This part is one of the major parts that got damaged. It has been 7 weeks and when we got our vehicle there is serious damage on the interior and exterior. Discovery as our insurer has not adressed our complaints or concerns anout Renew it. No one is adressing this problem. How can we trust Discovery with our vehicles?