Singapore Airlines — Theft of valuable from the baggage

Hello sir/ma'am,
Myself Jay shah travelling from Singapore to Mumbai via Kuala Lumpur
Flight number mh 0608 and mh 0194
Seat number 19f and 11f
I need to bring you in attention with the case of theft
When I received my luggage at the Mumbai airport I got a sense/doubt of my luggage been in abit doubtful condition but didn't took the matter seriously Bcz it was 3 am at night when I arrived and so left for home
After opening the luggage in the morning I found the case of missing watch worth 5digit
The box is opened/torn the watch is missing but I have the bill and guarantee/warranty card for the same.
Awaiting for quick response
I have been behind them from 4 days but still no proper response is been given.plz help