Hi JoiseMaMa,
I have already informed the management office. Today they came with the contractor upstairs to inspect my apartment. The contractor tried to shoulder off the responsibility in the first place. Subsequently he said he could not guarantee my walls will not crack again (of course I won't hold him liable in the future). Problem is my walls have been painted some years ago. Since he won't paint all the walls for me, the color of the paint will be different.
I asked the management office to take photos & inform the owner of the apartment upstairs. See if he has bought any 3rd party insurance which I doubt very much. If there is, the insurance company will send a surveyor or arbitrator to inspect my house, then we can proceed on the claim (or be denied! How can we prove it?). Sigh.... very troublesome as I plan to sell my apartment!!!!
This is a civil case. I am afraid the Police won't get involved.