Worst service ever

I took my car for service at Bosch Carnival. And I am very disappointed with their service. They have told me that my oil cap is leaking and needs to be replaced and it costs R800. And I gave them go ahead to replace it and to my surprise when I got home I found out that they have replaced it with an old cap. The level of dishonest of these people and their inflated prices is appalling because when I shopped around that cap is R115 and I paid R800 for used cap that according to them was new.