The responsibility for maintenance of a flat damaged by a leak from another flat

I've been having issues with my building management regarding a supposed leak from my flat damaging another property. I've contacted Rera with the following:

My building management is saying that there is a leak coming from my bathroom drain pipe which is damaging the below apartment. There is no leak inside my apartment. The only way to access the leak is to go through the below apartment's false ceiling as there is no possible way to access the drain pipe from my own apartment.

My building contract also does not mention anywhere that I would be responsible for paying for this kind of damage. I would like clarification on who is responsible! Also, the time that the leak was reported the flat was unoccupied.

Rera has replied that I am not responsible, however, the management company is still insisting.

Any ideas?