Service Master review: faulty service

hi
i am puneet bansal owner of maruti sx4 zxi model and i want to file a complaint against sevice master situated in jahangirpuri ssi industrial area in Newdelhi they had serviced my car in the month of october 2009, after that the gear and cluth of the car stop working and i file a complaint against it, they respond to my query really fast which is appreciable and the technical mentioned it to me that it is there fault and explained to me that they forget to put some kind of pin in the gear and you can use the car there is no problem in it after few months the cluth and the gear completely stop working when i went to them they give the bill of Rs20000 and now i am really confused and do not know what to do, i dont want to pay any money to them because it is not my fault and also i am taking this case to consumer court and also want you take some step against it please,

regards,
puneet bansal