Email Channel
For written issues, email is the best channel; topics like login and device changes are understood quickly when written in one line.
The same rule applies to messages sent from Dhaka; including screenshots and user IDs makes the answer clearer.
Live Chat
If you want a quick answer, use Live Chat; for small questions you don't need to open a separate thread.
If the night network is slow, open chat again later.
Mailing Address
If you need the address for official contact, you will find Dhaka-related information here; it is useful for paperwork or formal requests.
This reduces wrong messages, and makes it easier to know which department to write to.