Denying to provide service after payments

Location/place: Noida

Name of company/service: Ayush Motors

My Tata Indigo car broke down due to major problem in Car Engine in the month of November 2012. I got it repaired from Ayush motors and paid 50000 rupees for complete Engine work. Ayush motor delivered my car in January 2013 after repair with guarantee of 6 month for any wear and tear in car engine. It was running fine till now but It started giving trouble again on 30 April 2013. I went back to Ayush motors again with the problem statement. They did initial investigation of car and told me that there is problem in Car Fuel injector which his part of Car engine and I will have to 15000 approx for repair.
I want my car to be repaired without any charges as guaranteed by Ayush Motors (Authorized Tata Car Service provider). Apart from financial loss it is big mental trauma for me. I am tired of deal with Ayush motors illogical comments and lack of commitment in service provided by them.
My expectation is to fix my Car Engine problem once for all without any more charges since I already paid approx 50000 to Ayush Motors for the service done but still there are problems hence It is Ayush motors responsibility to fix it once for all and replace the faulty part to avoid any problem in future