Fiat India — Engine busted - oil burning

Website:

Hyson Fiat

I have a fiat linea emotion pack 2012 model. Run 67, 000 kms. All the services has been done from the agency with a belief that they will take care of the car. Iam getting my car serviced from hyson fiat, tichur, kerala.
At 67, 000 kms my car started burning oil. We took it to the service center and they had a examination and then topped up the oil and gave it back saying it is on observation. But again the same thing happened. When i dropped my car again for the same issue they said that a part replacement of the engine has to done. My car is under extended warranty (14/04/2016). When they claimed the for the warranty, it was rejected stating that the coolant was not changed on time.
My question is, when i am giving my car for services with the agency whenever the service is due, they should have intimated or changed the coolant or what ever oil has to be changed?. They are blaming us for not changing this at the right time.

They are going to charge 40, 0000 to 70, 000 after 20% discount, why should i bear these charges as my was under warranty .

I want my car fully repaired under my extended warranty.