Question

why did the sepoys refused to used the new cartridge

Answer 1

the sepoys refused because the cartridges were rumoured to be greased with the fat of cows and pigs which they had to bit off by the mouth before they were loaded into the rifle.

Answer 2

The new cartridges were unacceptable to the Indian sepoys, as they held the belief that these had been coated by the fat of cow and pigs. The sepoys had to bite the cartridges to load them. But their religion did not allow them to even touch these cartridges. Hence, they denied using the new cartridges.