Complaint to MAS against a financial institition

Read this webpage:
http://www.moneysense.gov.sg/publications/guides_publications/Consumer_Portal_Redress_Guide.html

Here is the online form
https://secure.mas.gov.sg/apps/wcmaweb/WebForm/WebCompForm.do

If you wish to write:

Monetary Authority of Singapore
Consumer Issues Division
Market and Business Conduct Department
10 Shenton WayMAS Building
Singapore 079117
Fax : (65) 6225-9766