Do something about this and lodge a complaint with the IDA by emailing the details to info@ida.gov.sg If SingTel is doing what you say they are then it's clearly a violation of the new Premium Rate Services code of practice (http://www.ida.gov.sg/doc/Policies%20and%20Regulation/Policies_and_Regulation_Level2/20070508145556/PRSvcCode.pdf)

Several smaller premium SMS providers have been fined already due to breaches - the IDA has some teeth here!