Leakage from above flat

There has been a leakage from above flat could be from their sink or bathroom, this has completely damaged my ceiling of hall passage and now kitchen, they are not willing to share the repair expenses. Who is really responsible to get the repairs of my flat done as it has been due to the leakage form over 4 months, is there any local.body who can help me with more details, I live in Mira rd Thanks