Then why does it keep happening and mods do nothing? Like with Teo En Ming?
There are various reasons:
1. A user may appear to be clone of the former that was banned, by mimicking behaviors and antics of the banned person. Yes, there are people who are that boliao.
2. User could have been banned, but has written in and requested to continue using the forums on condition that he/she behaves.
3. Users whose identity is ambiguous, e.g. suspected to be a clone but we are not able to conclusively prove from our systems that he/she is a clone.