Group 1 misdiagnosis causes costs.

After complaining about a broken diff (noisy and oil spewing out of it) Group 1 just replaced the oil and gave the vehicle back saying the problem was solved. on my first 4x4 gravel road trip I was astounded to find the diff shot. They and Mahindra claim that although the problem was reported during the warranty period my vehicle is now out of warranty and they will charge me for the repairs. This will not do.....