Update for people who may read in the future:
Management said they need to report to bring it up to IO meeting.
To get the report, technician said they need go to the flat upstairs.
The flat upstairs said they cannot allow private technician inside (but will allow from Buildings Department).
I can see management office not calling me back despite daily requests, and only answer once a day in WhatsApp.
I had an argument with them over the phone, and they told me to escalate to the Buildings Department.
I called 1823 and they will contact me back within 6 working days.
Hopefully, it will end well.