If the amount involved is as high as $300 million, it will be a serious allegation. But at the moment it looks like these are just rumors and you cannot confirm that these are true as your allegations do not show any valid evidence. You need more evidence to support your opinion. You can also call the police in the hope of reducing your losses.
Report to Singapore STRO or MAS
https://www.police.gov.sg/Advisories/Crime/Commercial-Crimes/Suspicious-Transaction-Reporting-Office
https://www.mas.gov.sg/regulation/enforcement/enforcement-actions
In the US you can try to contact the FBI or SEC
https://www.ic3.gov/Home/ComplaintChoice/default.aspx
https://www.sec.gov/
Hope it helps you.