IIRC they saw initial success but saw diminishing returns as it was figured out that they scare quite easily by fire, loud noises, pike formations, etc. If you manage to panic an elephant still in the enemy lines it can do quite some damage to their troops.

Hannibal did terrify Rome with them for a while, but Scipio Africanus figured out a very simple strategy to defeat them, which won the second Punic war for Rome at the battle of Zama. He just made corridors in his formation and channeled the elephants down them, which then ran away scared from the battle all together.

Those were Indian elephants, not the much larger and more aggressive African, and they were used in small numbers - 20 or so. The main defence was to scare them or to lure them into a bad position.

I'm envisioning all elephants working together with discipline and coordination which would make it nearly impossible to stop them.