What is the penalty for overcharging?

A Singapore Government Agency Website
For their own safety, drivers are advised not to pursue the fare evader. Instead, the driver should lodge a non-payment of fare report with his/her operator.
If drivers perceive an immediate risk to their safety:
Taxi drivers can activate the panic button installed in the taxi to alert the taxi company's call centre. The taxi company's call centre will be able to identify the location of the taxi through the GPS system, and alert other taxi drivers in the vicinity and police if further assistance is required.
PHC drivers can activate the emergency call feature on their ride-hail operator's mobile application or call the police directly for assistance.
Where possible, the driver should try to retain passenger and trip details (e.g. pick-up and drop-off points, further details provided to the driver through the booking such as passenger's name and phone number) and lodge the fare evasion case with his/her operator.
As a first step, the operator will attempt to contact the passenger to recover the fare, and thereafter reimburse the fare paid to the driver. If the outstanding fare remains unpaid and the passenger's identity can be established, the operator can refer the case to LTA and PTC for investigations.
The driver may also call the police for assistance or drive the passenger to the nearest Police Station, Neighbourhood Police Centre (NPC) or Neighbourhood Police Post (NPP). After lodging the police report, the driver can refer the case directly to LTA for investigation.