I had a full service in Dec 2009?

During this service i had a replacement alternator,waterpump and cambelt kit,its under warranty thank god and ive now had to have all 3 of those jobs done again in 9 months,i'm wondering if for 470 quid did I have second hand parts or just unversal fittings rather than vauxall Zafira comfort mpv 1999 parts has they havent lasted very long,there working on it still but i dont feel very confident as they said we may have to use vauxall parts instead,the kit came has being part plastic and they said they wasnt happy with the part has it should be steel im no mechanic so its over my head