Sorry, working overtime in highly competitive places like Singapore is very common. You are not alone as many Asian cities like Hong Kong, South Korea and Japan are like that.
There is nothing suspicious in your question. Working until the next day is not unusual, something that the Europeans here don’t understand. It’s part of the Asian working culture.
You are expected to work as long as your body can physical capable of. It will get better once you move into more senior position. Unfortunately, if you don’t obey you are not considered as employable.
For your records, my Asian friends would frequently work until 3 or 4 am just before the deadline. Your situation is not as bad as you might think.
The Singapore law allows you to say NO. You don’t have to work overtime if you really insist. But ... prepare for pressure, revenge and anger from your team as you're breaking the working culture and trust.
It’s bad if you are the only one leaving home early when the whole team stay late. Again, working late is absolutely expected in Asia.
- Leave the company
- Put the company to court
There is no point to talk to your boss again, as you've already done. It's not going to help.